Fix roomModule
Modify Database

- Rename delete{Model} to destroy{Model}.
- Emit 'destroyed' event when models destroyed.
- Delete current{Model} if the destroyed model is current{Model}.
- Don't Emit 'changed:current' event when current{Model}'s value is unchanged.
Let RoomPresenter check currentRoom
Send 'destroy:Room' when rooms destroyed
Fix bugs of Room#leave
Add a client side test of `room#leave`