Vid 2067

Using data attribute instead of script tag for retrieving gallery data. 
I find in little bit confusing that some "data" from "data" attribs is passed to createGallery as a parameter, but some other "data" is retrieved via "data" method inside createGallery.
Look at: https://github.com/Wikia/app/blob/VID-2067/extensions/wikia/MediaGallery/scripts/controllers/index.js#L8 and https://github.com/Wikia/app/blob/VID-2067/extensions/wikia/MediaGallery/scripts/controllers/index.js#L41