* Interaction object
   - void * pointer for interface specific stuff

* Widget object
   - for input, associated with a vlc_value_t

* Interaction manager
   - Maintains a list of currently active interaction displays
   - When a new interaction is requested, forward the request to the 
     interface (ASYNCHRONOUS !)
   - Asks the interface to show/modify/remove a display
   - Active polling ?

   - Signalling thhe interface : 
       - function pointer
		- easier to know if interface does not support
 		- 
       - variable
		- cleaner ? 
	- "control" function

* Requester 
   - Builds the interaction object
   - Add it to the interaction manager request queue. 
       - Queue or single with lock ?  
       - Analyze deadlock possibility