Only send presence updates to remote hosts if user is ours

Fix flake8 warnings for tests

Fix presence `currently_active`. Add presence metrics.

Rewrite presence for performance.

Mitigate against incorrect old state in /sync.

Remove dead code for setting device specific rules.

It wasn't possible to hit the code from the API because of a typo
in parsing the request path. Since no-one was using the feature
we might as well remove the dead code.

It wasn't possible to hit the code from the API because of a typo
in parsing the request path. Since no-one was using the feature
we might as well remove the dead code.

Merge all of the room membership codepaths into one

Conflicts:
	synapse/rest/client/v1/room.py

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... :(