Fix implementation of callbacks (update/stop)

[thgreasi]

This fiddle demonstrates some weird behavior with the callbacks provided to the sortable-options object.

• The $scope.model inside the update callback is not the new one, but the old one.
• The $scope.model inside the stop callback is the new one, but stop occurs after apply()

The only solution that I came up is: define a callback for stop, process the new data and call $scope.apply().

I think that the point of a callback, is to provide a way to respond to an event and
possibly process any changes that happened.
Those model-changes/new-model-state are not provided in any way in the current implementation.
(Obviously, nobody should have to call apply())

[alanheppenstall]

Thanks for your fix!

[thgreasi]

Why isn't this PR getting reviewed?
We are already using it on our production servers for over a month and seems stable.

[solidspark]

Apologies. Landed as 176ab1f.

[ProLoser]

@thgreasi do you have any interest in being added as a collaborator of this module?

[thgreasi]

Yes, of course!