Enhancement - Add ability to show custom button with return callback

[DigitalMystery]

When you have opened a specific image having the ability to have a custom button with a callback would be great (maybe on the left side opposite the "Done" button). I personally need the ability to flag images (which I'm sure would be helpful for other mobile applications).

`

<button class="button button-outline button-light close-btn" ng-click="closeModal()">{{::actionLabel}}</button>

`

Great work on this gallery, thanks

[pedroabreu]

There was a release allowing configurable template urls. I think the change needed now for this to happen is to allow passing scope functions to the directive.