Add AJAX callbacks for widgets events

[sgleizes]

Some of the wiQuery widgets have the ability to define AJAX callbacks for their events (like Tabs).
As I see no reason for this feature to be limited to a few, it would be nice to extend it to all the widgets.

Stephane Gleizes

[reiern70]

Patches are welcome. So, far we have added ones needed (asked) by users (including ourselves).