Add tests for get_latest_event_ids_in_room and get_current_state

Rather than adding them globally. This limits the changes to only
affect the tests.

Deduplicate membership changes

Set profile information when joining rooms remotely

Let users see their own leave events

Test that room membership is replicated

Add a slaved events store class

... otherwise clients get confused.

Fixes https://matrix.org/jira/browse/SYN-662,
https://github.com/vector-im/vector-web/issues/368

Don't require config to create database

Add a test to check that get_room_names_and_aliases does the same
thing on both the master and on the slave data store.

Move _get_cache_dict into the SQLBaseStore

Make the cache objects be per instance rather than being global

Separate generating the replication response...

Don't backfill from self

Fix stuck invites

from doing the http request parsing to make it easier
to write unit tests for replication.

If rejecting a remote invite fails with an error response don't fail
the entire request; instead mark the invite as locally rejected.

This fixes the bug where users can get stuck invites which they can
neither accept nor reject.

Store invites in a separate table.

Do checks for memberships before creating events

Use google style doc strings.

pycharm supports them so there is no need to use the other format.

Might as well convert the existing strings to reduce the risk of
people accidentally cargo culting the wrong doc string format.

Use a stream id generator for backfilled ids