Add `mouseover` and `mouseout` events to commonEvents

[malthejorgensen]

These seems like common events – why not let them be available by default? (there's probably something I'm missing)

[rtsao]

I think this is likely a performance optimization, but hopefully @Raynos can chime in.

You directly call DOMDelegator.prototype.listenTo if you need to.

For example:

var del = new Delegator();
del.listenTo('mouseover');
del.listenTo('mouseout');