Calculate empty seats for relocations

Added two methods to calculate empty seats for a school's current building and for it's proposed building in the case of relocations.  In the case of relocations, empty seats will use the new buildings ideal capacity.  

http://schoolcuts.org/schools/65
Lawrence is closing to Burnham.  Lawrence ideal capacity is 840 -  Burnham's enrollement is 268  = 572 empty seats.