CLC-1144 - [Front-end] - Clean up the CSS

https://jira.media.berkeley.edu/jira/browse/CLC-1144

* Underline on hover - button-links
* Fix focus on button links
* Update image replacement technique from html5boilerplate
* Prefix our classes/id's with cc-
* Splitting up files
* Remove unused CSS/Classes
* Convert IDs to classes for styling