Updated logic in MissionArea::getServerObject.

Before this function would iterate through every server-side object to
find a MissionArea. Now, it stores the server object in a static member
smServerObject. This member is updated in onAdd and onRemove, and returned
by getServerObject.
Merge pull request #140 from eightyeight/missionarea-server-object

Updated logic in MissionArea::getServerObject merged into development branch.