BS3: Restore Glyphicons

![mpw-49999](https://f.cloud.github.com/assets/98681/982305/08e11178-07e1-11e3-8ddb-bf3a2810f921.jpg)

After going back and forth on this for the last couple weeks, I've decided to restore the Glyphicons icon font to the main repo. Given how prevalent icons are in UIs, it's probably a disservice to most folks to not include them (or some other icon font) in the same spot as the CSS and JS.

With this update comes the following:

* Restore documentation (on the Components page)
* New variables, `@icon-font-path` and `@icon-font-name`, for flexibility in adding and removing icon fonts
* Removes the old Glyphicons mention from the CSS page

We'll work on improving the customization of icon fonts in the future so swapping font libraries can be easier (which was the whole motivation for the original removal).