Expose "run_foo_callbacks" callbacks api

I noticed you cheating in abstract controller. We are abusing our own api rules by calling a private "_" method in a different module.

    def process_action(method_name)
      _run_process_action_callbacks(method_name) do
        super
      end
    end

It should be using "run_callbacks :process_action". However, think we should just fully expose the nicer generated methods as the public api.

• Rename "_run_foo_callbacks" to "run_foo_callbacks"
• Document it as the main api
• Put a deprecation notice in "run_callbacks"