Removed old and unused feature headers
	deleted:    ../vision/FeatureFilter.h
	deleted:    ../vision/FeatureMatcher.h
	deleted:    ../vision/FeatureRowLookupContainer.h
Change usage of GFXEngine and Drawable interface

	modified:   ../gfx/GFX.cpp
	modified:   ../gfx/GFX.h
	modified:   ../gfx/Image.cpp
	modified:   ../gfx/Image.h
	modified:   Widget.cpp
	modified:   Widget.h
	modified:   Window.cpp
	modified:   Window.h