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 
As you said "If the options are set, they are booleans, otherwise, being optional, they are undefined" - but whoever will be extending/maintaining that code in case of wanting to check if lazyload is disabled shouldn't have to worry if it is disabled because of the default or because of the desired configuration being passed. Currently check like ```if ( this.lazyload === false )``` wouldn't work - someone would have to use two equals instead of three, or check if not true - but that requires deeper knowledge about implementation details.