Wicket 6.0 support

Hello, i did try to migrate visural to wicket 6.4. If interrested you could pull the branch. 

- did upgrate to wicket 6.4
- did add a grandle build file, coz was not able to build the project via ant.
- did not really test anything ... 

I use the RichTextEditor, @At and Confirmer link so this looks allright. Not sure about the rest :)