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 
I would personally go for:
```(new LightboxController({ model: data }))) .init();```
and skip creating and initializing lightboxController variable altogether, but not that important