$swipe now sends a cancel event when the mouse leaves the element

There was a problem with $swipe and mouse events. When the user reaches the limit of the element while swiping and comes back, the swiping is still active, even if the user released the mouse button while outside the element.

This pull request prevent this "stickiness" from happening.

Ideally we would be able to swipe outside the element if we started the swipe inside, but that would mean binding events to the document. And I believe directive try to avoid that as much as possible