GinUiBinder update for GWT 2.5

This may be a breaking change (it always is). If someone could test with GWT 2.4, it would be appreciated.

CarStore has been updated to use an injected widget. Everything is back and running.

I've also modified slightly the GWT classes to allows overwriting what was needed to promote those changes in GWT in the future.

A note that is worth saying, make sure that you inherit GWTP before GWT in your classpath. In maven if GWT is defined before GWTP, it won't work as it will take the GWT UiBinder generator instead of the GWTP.

To activate GinUiBinder, you must add:     ```<inherits name="com.google.gwt.uibinder.GinUiBinder" />```

In you .gwt.xml