Medal improvements

Miscellaneous improvements to the medal system and code in general. Most notably, players now receive medals in the background even when the client has cl_medals disabled, and the server now synchronizes every player's medal count to clients receiving a full update. The code for drawing received medals on the screen has been refactored too and no longer assumes that the medal's icon is offset at its centre, as is the case with the Skulltag medal sprites (which have been fixed a bit too).