Started on implementing rest action handlers.
Major refactoring to the client action handler system, see below:
* Renamed the system 'client action handlers' to 'interceptors'.
* Moved the standard functionality with some enhancements to the rpc package.
* Implemented functionality for rest interceptor support.

TODO:
* Create a full set of tests to ensure it's working.
* Fix javadocs and any remnants from the previous naming convention.
Added Builder class for InterceptorContext.
Merge branch 'master' of github.com:ArcBees/GWTP into interceptors_squash2

Conflicts:
	gwtp-core/gwtp-dispatch-rest/src/main/java/com/gwtplatform/dispatch/rest/client/DefaultRestDispatchCallFactory.java
	gwtp-core/gwtp-dispatch-rest/src/main/java/com/gwtplatform/dispatch/rest/client/DefaultRestDispatchHooks.java
	gwtp-core/gwtp-dispatch-rest/src/main/java/com/gwtplatform/dispatch/rest/client/RestDispatchCall.java
	gwtp-core/gwtp-dispatch-rest/src/main/java/com/gwtplatform/dispatch/rest/client/gin/RestDispatchAsyncModuleBuilder.java
	gwtp-core/gwtp-dispatch-rpc-client/src/main/java/com/gwtplatform/dispatch/rpc/client/DefaultRpcDispatchCallFactory.java
Keep backwards compatibility for ClientActionHandler's.
Merge pull request #597 from BenDol/interceptors_squash2

Replace 'Client Action Handlers' with 'Dispatch Interceptors'