Add oninfo control action

This adds a new action ```oninfo``` for controls. The action will only be executed if there is no default info action, e.g. show movie information. Skinners will be able to do some nice things with it and won't need to sacrifice a navigation action (left, right, up, down).

Some examples:
- Show extended info for recently added lists on the home screen
- Open metadata actors info in the actors list
- Show application information in the advanced launcher add-on

Hope this will be added to Gotham.