Vid 2079 prep gallery JS for outside usage

Setting up a better entry point for VE to consume media galleries. Now, in order to instantiate galleries, simply recreate the logic in controllers/index.js in whatever environment it is needed. 

@inez 
@lizlux currently yes - you are checking only for falsey values - however as you specify in the comment, options are supposed to be booleans, so in the future whoever will be extending the code might run into problem when checking for instance ```if ( this.lazyload === false )```
Is there any reason why not to do it other than it does not provide value right away?