Convert Styles to SASS

**Optimize structure and CSS files using SASS**
## Converted ``css`` files to ``scss``
* Add all missing vendor prefixes for Chrome, Opera, Firefox, IE using Compass
* Add configuration through SASS variables in ``_photobox-variables.scss`` file
* Separate media queries and animations using partials
* Include minified and non-minified css versions
* Optimize CSS using ``@extends``.  Remove/combine many duplicate selectors.

## Structure Changes
* Restructure folder structure to have a ``demo`` folder, so it's clear that it's the demo
* Remove need for supporting IE.  There were not enough lines to justify a separate file.
* Create/rename image folders as needed