This button is currently hidden under the user menu, but it should be
shown more prominently - especially under the Devices settings. The
button under the user menu and this new one is now hidden when your
device is already verified.
Use the forget function to leave a room everywhere this is both for consistency and to reduce dependencies. This way no dependency on RoomManager is required to leave a room and since in all cases they have an object they can just call the function.
To make this work `AccountManager` is split off from controller taking all the code around `AccountRegister` and is added to LibNeoChat as it makes sense to have this functionality there.
