Adding Backbone app for UI

Added index.html and all the public assets, including a Backbone app
that builds the grunticon assets using canvg, JSZip, and the File API.
Fixed problem with zipped PNGs

JSZip needs the image data without the `data:image/png;base,` part.
Minor changes to index.html
Split file previews into separate views
Cleaned up some styles
Fixes to preview.html and icons.fallback.css

preview.html was escaped, now should be html. icons.fallback.css was
showing the wrong css.
Unescaped the JS in preview.html
Merge pull request #2 from ericponto/master

Added front-end of the app