fixes #317

This was a bit of a journey:
https://github.com/matrix-org/matrix-doc/pull/3471
But it should work now and we now use the UIAHandler everywhere.

fixes #670

This ports the leave room dialog to QML, everywhere. There are now no differences between the various leave dialogs.

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

Room Directory UI for exploring and joining public rooms. V1: simplistic server + network facilities

There are probably a few things wrong with this, but I'm going to call it good enough for an initial commit

This also adds a property `roomId` to TimelineModel.