Config file to store game informatino.

Currently contains board width, cell size, and image locations.
XMLReader

Proxy class to boost::property_tree::ptree
new class: Configuration.

Singleton class to store game configuration data. Loads data from config.xml on initialization.

The code for this will be cleaned up; this is just temporary.
Modified GraphicsHandler and AppStateGame to use Configuration, instead of declaring hardcoded paths.
Fixed some includes in Piece.h

updated .gitignore
Merge remote-tracking branch 'origin/dirty' into dirty