Fixing phonegap with REST dispatcher

The application was just never tested with REST dispatcher and phonegap.
I tested using emulate.phonegap.com and gwtp-carstore.appspot.com, and everything seems to work pertty much out of the box. You only have to bind the RestApplicationPath to the correct path.

I'm not sure if the RestDispatchAsyncModule.Builder class is really usefull. It seems to give more versatility to use annotations bound constants