BROKEN Work in progress for adding event Amenities

BROKEN Work in progress for adding event Amenities

Amenities are added to the Edit Event form - but they are not
functional. A new amenity can be added successfully but is then
not attached to the event.

The "Add a new amenity" popup currently has a needless dropdown
but needs to optimally be like the "Add an amenity" in the member
DB settings. It will in fact -not- be like the category button in
that it shall nto have a parent, but needs to show the amenity
groups, which are not yet properly handled in the model.

Then the corresponding button for adding amenities, along with the
one for adding categories, needs to not be displayed if the user
lacks admin privileges.