Added class Data::Ability and made all code use symbols for abilities instead of numbers. Also added class Data::Item but it's unused.

Data/Scripts/017_UI/013_PScreen_Load.rb

@@ -268,6 +268,7 @@ class PokemonLoadScreen
       $scene = nil
       return
     end
+    Data::Ability.load
     commands = []
     cmdContinue    = -1
     cmdNewGame     = -1