Mobile/responsive CSS for the dashboard

Affects body.projects-index, body.finalists-index.

- Setting the device-width viewport on appropriate pages and various widths to not exceed it
- Header nav is hidden by default, with a hamburger button
- User/admin nav is hidden by default, with a hamburger button
- Individual projects are restyled to fit compactly, with different pink and blue highlighting styles

Awesomebits issue #77