Hotfixes v0.8.1 r3

Don't yield on notifying all listeners

Fix a notifier leak

Add paranoia checks to make sure that we evict stale NotificationListeners when we are about to process them

Fix bug where we didn't inform the NotificataionListeners about new rooms they have been subscribed to. This meant that the listeners didn't clean themselves up fully from all the dicts

Caused by a bad if check, which incorrectly executes for both 0 and None,
when None was the original intent.

Specifically, the ASes own user ID wasn't being treated as 'exclusive' so
a human could nab it. Also, the HS would needlessly send user queries to the
AS for its own user ID.

Application services registration changes (PR #116)

This was caused by not explicitly checking the service.sender field. This
has now been fixed and a regression test has been added.

Form the user ID at runtime instead, This gives less room for error in AS
config files since they cannot specify the domain of another HS.

turn --disable-registration into --enable-registration, given the default is for registration to be disabled by default now. this is backwards incompatible by removing the old --disable-registration arg, but makes for a much more intuitive arg

This reverts commit ff1fa0fb.

Allow registration in the HSes federation demo