Use a stream id generator to assign state group ids

Require user to have left room to forget room

This dramatically simplifies the forget API code - in particular it no
longer generates a leave event.

Add new author

Support login using Javascript Web Tokens (JWT)

Deduplicate identical /sync requests

Never notify for member events.

Intern lots of strings

Don't require alias in public room list.

Make get_invites return RoomsForUser

Only cache events in the event cache

Make StateHandler._state_cache only store event_ids.