GWT-597 simplified loading screen editor refactoring loading screen
GWT-597
Merge remote-tracking branch 'origin/GWT-597' into GWT-597

Conflicts:
	plugin/deskmanager/deskmanager-gwt/src/main/java/org/geomajas/plugin/deskmanager/client/gwt/common/editor/loadingscreen/LoadingScreenImageEditor.java
	plugin/deskmanager/deskmanager-gwt/src/main/java/org/geomajas/plugin/deskmanager/client/gwt/common/editor/loadingscreen/LoadingScreenImageInfo.java