Nifty Editor integration 

Hello, this pull request adds the new visual editor for nifty-gui files. This is the result of the JME Soc project, also there is a detailed devblog about the implementation in (this)[http://hub.jmonkeyengine.org/forum/board/development/summer-of-code/] sub forum. In particular this pull requests contains new features such as : 
- A new palette
- New visual editor with real time manipulation of elements
- Templates for : A basic nifty-gui, an empty nifty-gui , empty style , control and button style.
- Navigator to see the gui structure
- Undo support
- Copy&Paste actions
- Save changes

The project contains all the classes needed to integrate the editor in SDK platform all the logic to edit nifty files resides inside nifty-editor project which this project depends.
I hope this is details is enough!