Fixed DispatchHooks binding when using both dispatchers

One of the reason I'm not sure about the DispatchHooks class. Using bindAnnotated with it seems wrong because I'm not sure why you'd want to have multiple hooks class (plus the user would have to inject it with either `@RestBinding` or `@RpcBinding`), and protecting double-binding is a bit weird, because the Builder class for each Dispatcher makes you think you can have different hooks for each Dispatcher. I'm not sure which is best..  
@spg @Chris-V @christiangoudreau