Remove external rooms

[daronco]

External rooms are rooms that exist in the web conference server but that are not in the database. This happens only when meetings are created in the web conference server using something else other than Mconf-Web.

This feature is very likely not used at all and brings some extra complexity to the code. For instance, any operation over a room that changes attributes and saves the room needs to check whether the room is already in the database or not (new_record?).
If external rooms are really not used, removing it would make the gem a bit simpler.