Add a Homeserver.setup method

Make it possible to paginate forwards from stream tokens

In order that we can fill the gap after a /sync, make it possible to paginate
forwards from a stream token.

Remove redundant BaseHomeServer

Fix federation for #test:matrix.org

... rather than rejecting any attempt to federate channels which contain such
events.

Fix adding push rules relative to other rules

This is for setting up dependencies that require work on startup. This
is useful for the DataStore that wants to read a bunch from the database
before initiliazing.

Only notify for messages in one to one rooms, not every event

Fixes the fact that candidate events and hangups generated notifications.

Add missing yield in push_rules set enabled

Move some sync logic from rest to handlers pacakege