Replace icon images with icon font

We need to look at how existing icon fonts have been doing it:

* https://github.com/twitter/bootstrap/blob/3.0.0-wip/less/glyphicons.less
* https://github.com/FortAwesome/Font-Awesome/tree/master/build/assets/font-awesome/less

Here's the current iteration of the icon font: [https://dl.dropboxusercontent.com/u/905197/GB_icon_font.zip](https://dl.dropboxusercontent.com/u/905197/GB_icon_font.zip)