Start work on avoiding table locks for upserts

Now that _simple_upsert will retry on IntegrityError, we don't need to lock the
table.

wrap the call to _simple_upsert_txn in a loop so that we retry on an
integrityerror: this means we can avoid locking the table provided there is an
unique index.

Bail out early to reduce indentation

Pull out bits of StateStore to a mixin

Declare support for r0.3.0

Remove preserve_context_over_{fn, deferred}

Rename redact_content option to include_content

update prometheus-config to new format

This restores the config that is usable for prometheus pre v2.0.0
The new config only works for Prometheus v2+

Reshuffle room list request code

Add new boolean columns to port script

... so that we don't need to secretly gut-wrench it for use in the slaved
stores. I haven't done the other stores yet, but we should. I'm tired of the
workers breaking every time we tweak the stores because I forgot to gut-wrench
the right method.

fixes https://github.com/matrix-org/synapse/issues/2655.

We're going to fix this properly on this branch, so that the _state_group_cache
can end up in StateGroupReadStore.

This reverts commit ab335edb.

Make __init__ consistent across Store hierarchy

Both of these functions ae known to leak logcontexts. Replace the remaining
calls to them and kill them off.

I'm not entirely sure if this will actually help anything, but it simplifies
the code and might give further clues about why room list search requests are
blowing out the get_current_state_ids caches.

So we can see what it gets up to.

Add a route for determining who you are

Signed-off-by: Travis Ralston <travpc@gmail.com>

Cache failures in url_preview handler

Fix 500 on invalid utf-8 in request

because we had to wait until the logger was set up

Fix the test to pass the right number of args to the Store constructors

Add db_conn parameters to the `__init__` methods of the *Store classes, so that
they are all consistent, which makes the multiple inheritance work correctly
(and so that we can later extract mixins which can be used in the slavedstores)

This reverts commit f5cf3638.

Useful for applications which may have an access token, but no idea as to who owns it.

Signed-off-by: Travis Ralston <travpc@gmail.com>