Implement CFA Styleguide styling for admin interface

[nihonjinrxs]

Implement styling consistent with the Code for America styleguide for the Administrative user interfaces provided by the API.

For maintenance reasons, we cannot use the existing styleguide gem, as we cannot support BEM-style CSS for the UI in this app.

This issue is a starting point for the UI transition, which likely includes the following:

• [ ] Identifying any existing UI that does not match the style guide
• [ ] Creating issues for each deviation
• [ ] Fixing each deviation, or identifying in the issue why it is difficult or impossible to do so

Note: This should not impact the API JSON views, which should remain the same after this update.