Created ScreenSpace model

• Created ScreenSpace; it's (currently) a clone of GeoSpace (since both are placeholders for general, singlular concepts).
• In GeoSpace, renamed sSharedGeoSpace to sSharedInstance since the general concept is more important internally than the type and there's no possibility of conflict.
• Added ScreenSpace to the project file, by hand.
• Added tests in SpaceModelTests matching GeoSpace's for ScreenSpace.
Merge branch 'adhoc/travis-build-test' into feature/unit-models