I'm not particularly happy with the "action" switching, but there's no
convenient way to defer the work that needs to happen after it, so... :(

Currently, we magically perform an extra database hit to find the
inviter, and use this to guess where we should send the event. Instead,
fill in a valid context, so that other callers relying on the context
actually have one.

Conflicts:
	synapse/handlers/room.py

Simplify room creation code

Unclean, needs tidy-up, but works

Also, consistently apply rate limiting.

Again, ugly, but a step in the right direction.

This code is kind of rough (passing the remote servers down a long
chain), but is a step towards improvement.

Force joining by alias to go through the send_membership_event checks,
rather than bypassing them straight into _do_join. This is the first of
many stages of cleanup.

This reverts commit cf81375b.

It subtly violates a guest joining auth check

Merge two of the room join codepaths

There's at least one more to merge in.

Side-effects:
 * Stop reporting None as displayname and avatar_url in some cases
 * Joining a room by alias populates guest-ness in join event
 * Remove unspec'd PUT version of /join/<room_id_or_alias> which has not
   been called on matrix.org according to logs
 * Stop recording access_token_id on /join/room_id - currently we don't
   record it on /join/room_alias; I can try to thread it through at some
   point.

There's at least one more to merge in.

Side-effects:
 * Stop reporting None as displayname and avatar_url in some cases
 * Joining a room by alias populates guest-ness in join event
 * Remove unspec'd PUT version of /join/<room_id_or_alias> which has not
   been called on matrix.org according to logs
 * Stop recording access_token_id on /join/room_id - currently we don't
   record it on /join/room_alias; I can try to thread it through at some
   point.

Catch the exceptions thrown by twisted when you write to a closed con…

Enforce user_id exclusivity for AS registrations

This whole set of checks is kind of an ugly mess, which I may clean up
at some point, but for now let's be correct.

Return events in correct order for /events