Invite users to existing rooms
Scope:
- Allow inviting from the room detail screen and the member list
- Invite option is only shown if the user has the correct power level
- Search flow the same as creating a new room, allowing multi-select
- Existing room members/invitees are disabled with a custom caption
- Sending is asynchronous, an error dialog will appear wherever the
user is if necessary
Closes#245
* Implement room member list
* Move timeline initialization back to `TimelinePresenter`.
* Fix crash when the `innerRoom` inside a `RustMatrixRoom` is destroyed but `syncUpdateFlow` is still running.
* Address review comments
