Moved stylesheets to Sass and fixed broken styles

Moved the stylesheets to Sass and fixed some of the styles that were "broken" (e.g. the user menu in the top right was overflowing its container and the ribbon for the "Learn more" button on the homepage was moving around awkwardly).

Also:
- Added the Open Sans font to the project to no longer require pulling it from Google's servers
- Moved the images into `public/imgs` from `public/images` (as a *micro*-optimization :disappointed:)
- Optimized all the images in `public/imgs` (i.e. I ran them thru CodeKit)
- Told Git to not show diffs for SVG and CSS files (see the `.gitattributes` file)
- Removed the leading zeros from the user schedule table view
- Modified the markup for the register form to place labels after checkboxes and radio btns, as required for styling

Most importantly: everything *should* look the same as before.

I still want/need to make the grid fluid (this would probably be done best/easiest by using a framework like [Foundation](http://foundation.zurb.com/). Doing so would lend itself well to a more smaller-screen-friendly layout, and keep the the same look and feel, but be a bit more "responsive".

Closes #7 when/if accepted.