Add support for 9-patch images
[WPF] Bitmap support fixes

Properly implemented image cropping.
Implement GetScaleFactor.
NinePatchImage: Improve detection of stretchable areas
Added unit tests for 9-patch images

Also fixed some rendering issues in gtk.
Fixed rendering of 9-patch images in retina resolution
Add missing test files
Add WPF test image files
[WPF] Fixed 9-patch rendering issues

And added tests.
Merge branch '9patch'