Create index.html, gallery.css, and gallery.js

Committing completed responsive image gallery.

A significant challenge for creating this gallery was how little instruction was provided for desired functionality. Was fluidity and animation important? Or was this more of a back-end exercise? In the end, with the understanding that time was of the essence, it seemed most reasonable to create a simple gallery that would display one large image and thumbnails of everything else via JSON. At the mobile level, all images are displayed along with the rest of the appropriate textual info from the JSON file. With that in mind, straight JavaScript was used without any jQuery to bog things down, so there is no animation. The reponsive element is handled entirely in CSS. The JSON is pulled in via AJAX, but used synchronously, in order to allow processing as an object. What ended up taking the longest was playing around with the the js AJAX calls, as it had been a while since I had last done anything like that without jQuery, which seems ubiquitous these days.