This avoids the scenario where we have four different PreviewUrlResources
configured on a single app, each of which have their own caches and cache
clearing jobs.

* Improve documentation of workers

Fixes https://github.com/matrix-org/synapse/issues/2554

Fixes https://github.com/matrix-org/synapse/issues/2554

Clean up dependency list

Avoid locking account_data tables for upserts

remove those that aren't used at all, and replace the ones that don't have
builders with simple getters rather than dynamically-generated methods.

Avoid locking for upsert on pushers tables

Add automagical AS Publicised Group(s)

* replace the upsert into deleted_pushers with an insert
* no need to lock for upsert on pusher_throttle

This PR was against master, not develop :(

This reverts commit 203058a0, reversing
changes made to 552f123b.

Fix auth handler

via registration file "users" namespace:

```YAML
...
namespaces:
  users:
    - exclusive: true
      regex: '.*luke.*'
      group_id: '+all_the_lukes:hsdomain'
...
```

This is part of giving App Services their own groups for matching users. With this, ghost users will be given the appeareance that they are in a group and that they have publicised the fact, but _only_ from the perspective of the `get_publicised_groups_for_user` API.

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