Separate XWiki Google Web Toolkit projects from xwiki core code

The objective is to be able to separate new XWiki GWT projects from the xwiki core and be able to work on them and build them using maven2
We need for this:

• create an xwiki-gwt module with the server side API in the core
• build this module using maven2

• create external projects in xwiki-apps using google web toolkit
• being able to build them using maven2
• being able to build them and debug them using IntelliJ