Bug 1070001: Re-org Stylus

- Switched from @import to @require.
- Files should now @require the files they need rather than relying on an @require in a parent include.
- Files in /include should not generate output.
- Tried to break files in main into sensible smaller pieces.
- Renamed /main to /base to better communicate its function (hopefully this will do away with my brain tick that thinks the global nav stuff belongs in this folder).
The red marker means that there isn't an (invisible) newline at the end of the file. EditorConfig should have created this. If it doesn't, a new line can be added manually. A text editor might show it as an actual line, taking up space, but once here on GitHub it should only be apparent by the absense of this icon.