This module links partners with the events they are registered through a
smart button.

It also includes:

* Search partners by their event attendees.
* Search partners by number of events attendees.
* Search partners by number of events attended.
* Partner column is visible on registration one2many list inside the event.
* Action in partner tree view 'More' button, to register several partners
  to an event
* Restricts partner deletion when event attendees are linked to it.
* Onchange for partner_id removed in v16 core in Event Registration- including functionality here
