Fixes in GWT backend:
-added log configuration with GwtApplicationConfiguration.log
-more accurate value of GwtGraphics.getDensity()
-Skin emulation takes NinePatch padding into account (copy-paste from not emulated class)
-fixed filtering of asset files in PreloaderBundleGenerator
Merge pull request #288 from kreymerman/gwt_fixes

Couple of small fixes in GWT backend