Beautification pass 2

 - Nicked some background transition code from an old project of
   mine.
 - Background color now changes alongside whoever's turn it is.
 - Now with Google Fonts!
 - You can now choose between 3 different quality levels, so potato
   computers can get in on the fun too.
 - On medium and high quality levels, cells now transition, which
   generally looks easier on the eyes and is easier to follow
   what's happening (especially when the last player makes their
   move and the board updates.)
 - General CSS file cleanup.