Changed the scope of side controller lock.

The lock is now per side, not per scenario. The lock has also been
renamed to "controller_lock".

Additionally, the game should now not apply a lock if "controller"
attribute was empty.
Refactored a method in mp::connect_engine.
Added "controller_lock=no" for multiplayer maps.

These changes guarantees that it will be possible to select any kind of
controller in MP Connect screen in all multiplayer maps.
Added missing side attributes to team::attributes array.