Allow user-generated stylesheets

Feature request

It would be awesome if users had the option of pointing to a local, custom stylesheet that took precedence over base.css. Ideally, there would be an additional environmental variable/setting called CUSTOM_CSS_PATH (or similar). This would give users more control over the look and feel of Mayan EDMS, and would allow designs to be shared between users easily.

Bonus: Create a public repo for users to contribute their stylesheets. This would allow those who are less well versed in CSS to pick and choose a design they like. This could also serve as a stash of design inspiration for the development team here.