Fixes messages in room flickering and being stuck

fixes #760
relates to #770
relates to #789

Showing the bootstrap state and showing there are unverified devices is
still missing.

Added support for refreshing the device list, marking current device with a checkmark instead of a lock

There is not really a reason to stop tracking them, just because the
server says so. We might still want to show a users profile, etc.

This fixes spaces or stickers not showing up for old databases as well
as the wrong format of the state_keys db.

Also fixes some issues where nested transactions will poison the
verification cache.

fixes #636

Nested QEventLoops are scary. Ultimately we shouldn't use them, but I
have no better solution right now.

fixes #656