Add some options (videos handling, layout and selection ordering)

[zepojo]

This makes the component more customizable, by allowing the user to change some options. These options can be set through a configuration proxy (YMSPhotoPickerConfiguration) and are the following:

• sourceType: the type of media that can be browsed, captured and selected by the user. This makes YMSPhotoPicker compatible with videos.
• numberOfColumns: the number of columns of thumbnails visible when browsing the gallery.
• sortingType: the way selected medias are sorted in the delegate callback method, and the kind of check displayed on every selected cell (check mark or label of the order).

I don't know if the fact that the component was only compatible with photos was what's intended, but the video compatibility can make it more powerful. Every part of the lib been adapted (grid cells, preview screen, camera mode and delegate methods). The default options make the component act just like it is today.

[yahoocla]

Thank you for submitting this pull request, however I do not see a valid CLA on file for you. Before we can merge this request please visit https://yahoocla.herokuapp.com/ and agree to the terms. Thanks! :smile:

[yahoocla]

CLA is valid!

[fryette]

@ink-spot could you please fix merge request? I would like to port it to the xamarin binding library. Thx in advance