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

https://jira.media.berkeley.edu/jira/browse/CLC-1144

* Start partials with _
* Do `import "test"` instead of `import "test.scss"`
* Combine the classes and groups css
* Separate out the footer & header
* Remove unused CSS
* Renaming
* Use the new version of linear gradients - use background instead of background-image!

** This doesn't fix the jira yet, it's just one step in the process**