We need to make sure we are readu for the `set_cache_factor` callback.

* Add `DeferredCache.get_immediate` method

A bunch of things that are currently calling `DeferredCache.get` are only
really interested in the result if it's completed. We can optimise and simplify
this case.

* Remove unused 'default' parameter to DeferredCache.get()

* another get_immediate instance

rather than have everything that instantiates an LruCache manage metrics
separately, have LruCache do it itself.

This implements a more standard API for instantiating a homeserver and
moves some of the dependency injection into the test suite.

More concretely this stops using `setattr` on all `kwargs` passed to `HomeServer`.

Optionally sends typing, presence, and read receipt information to appservices.

These are tests for #8439

* Fix outbound federaion with multiple event persisters.

We incorrectly notified federation senders that the minimum persisted
stream position had advanced when we got an `RDATA` from an event
persister.

Notifying of federation senders already correctly happens in the
notifier, so we just delete the offending line.

* Change some interfaces to use RoomStreamToken.

By enforcing use of `RoomStreamTokens` we make it less likely that
people pass in random ints that they got from somewhere random.

Update `EventCreationHandler.create_event` to accept an auth_events param, and
use it in `_locally_reject_invite` instead of reinventing the wheel.

Support returning a new event dict from `check_event_allowed`.

this is always the same as requester.access_token_id.

Should fix #3365.

Currently background proccesses stream the events stream use the "minimum persisted position" (i.e. `get_current_token()`) rather than the vector clock style tokens. This is broadly fine as it doesn't matter if the background processes lag a small amount. However, in extreme cases (i.e. SyTests) where we only write to one event persister the background processes will never make progress.

This PR changes it so that the `MultiWriterIDGenerator` keeps the current position of a given instance as up to date as possible (i.e using the latest token it sees if its not in the process of persisting anything), and then periodically announces that over replication. This then allows the "minimum persisted position" to advance, albeit with a small lag.

This could, very occasionally, cause:

```
tests.test_visibility.FilterEventsForServerTestCase.test_large_room
===============================================================================
[ERROR]
Traceback (most recent call last):
  File "/src/tests/rest/media/v1/test_media_storage.py", line 86, in test_ensure_media_is_in_local_cache
    self.wait_on_thread(x)
  File "/src/tests/unittest.py", line 296, in wait_on_thread
    self.reactor.advance(0.01)
  File "/src/.tox/py35/lib/python3.5/site-packages/twisted/internet/task.py", line 826, in advance
    self._sortCalls()
  File "/src/.tox/py35/lib/python3.5/site-packages/twisted/internet/task.py", line 787, in _sortCalls
    self.calls.sort(key=lambda a: a.getTime())
builtins.ValueError: list modified during sort

tests.rest.media.v1.test_media_storage.MediaStorageTests.test_ensure_media_is_in_local_cache
```

This PR allows Synapse modules making use of the `ModuleApi` to create and send non-membership events into a room. This can useful to have modules send messages, or change power levels in a room etc. Note that they must send event through a user that's already in the room.

The non-membership event limitation is currently arbitrary, as it's another chunk of work and not necessary at the moment.

All handlers now available via get_*_handler() methods on the HomeServer.

We call `_update_stream_positions_table_txn` a lot, which is an UPSERT
that can conflict in `REPEATABLE READ` isolation level. Instead of doing
a transaction consisting of a single query we may as well run it outside
of a transaction.

We call `_update_stream_positions_table_txn` a lot, which is an UPSERT
that can conflict in `REPEATABLE READ` isolation level. Instead of doing
a transaction consisting of a single query we may as well run it outside
of a transaction.

This allows a user to store an offline device on the server and
then restore it at a subsequent login.

Lots of different module apis is not easy to maintain.

Rather than adding yet another ModuleApi(hs, hs.get_auth_handler()) incantation, first add an hs.get_module_api() method and use it where possible.

* Optimise and test state fetching for 3p event rules

Getting all the events at once is much more efficient than getting them
individually

* Test that 3p event rules can modify events

Per https://github.com/matrix-org/matrix-doc/pull/2788

PR #8292 tried to maintain backwards compat with modules which don't provide a
`check_visibility_can_be_modified` method, but the tests weren't being run,
and the check didn't work.

This is now redundant, and we can just call `handle_new_client_event` directly.

This PR allows `ThirdPartyEventRules` modules to view, manipulate and block changes to the state of whether a room is published in the public rooms directory.

While the idea of whether a room is in the public rooms list is not kept within an event in the room, `ThirdPartyEventRules` generally deal with controlling which modifications can happen to a room. Public rooms fits within that idea, even if its toggle state isn't controlled through a state event. 

This is so we can tell what is going on when things are taking a while to start up.

The main change here is to ensure that transactions that are created during startup get correctly logged like normal transactions.

This allows for connecting to certain IdPs, e.g. GitLab.

The idea is that in future tokens will encode a mapping of instance to position. However, we don't want to include the full instance name in the string representation, so instead we'll have a mapping between instance name and an immutable integer ID in the DB that we can use instead. We'll then do the lookup when we serialize/deserialize the token (we could alternatively pass around an `Instance` type that includes both the name and ID, but that turns out to be a lot more invasive).