Renamed private sessions field to userSessions in GanymedeServer

This helps emphasize the limited nature and purpose of the
userSessions Vector, which only tracks GanymedeSessions which
are shown in the admin console.
Simplified a Vector copy in GanymedeServer.setShutdown()
Removed some unneeded imports in GanymedeServer
Modernized a few Vector calls in GanymedeAdmin
De-synchronized login methods on GanymedeServer

After doing the refactoring to simpler methods, it appears
pretty clear that there is no reason that the processLogin(),
admin(), validateUserLogin() and validateAdminLogin() methods
need to be synchronized at this level.

Queries on the loginSession object are already serialized/synchronized,
and the DBQueryEngine uses the DBLock system to make sure that the
actual queries are thread safe with respect to transaction commit.
Cleaned up GanymedeServer.admin() method

Added the default localization strings for documentation
purposes, removed a seemingly trivial comment about
GanymedeAdmin construction.
Took out a vestigial comment in GanymedeServer.processLogin()
Comments in DBStore
Cleaned up our pluralized event object names