[WIP] Bug 1036486 less2stylus

See https://bugzilla.mozilla.org/show_bug.cgi?id=1035783

[staticfiles](https://github.com/mozilla/olympia/pull/110) PR needs to be landed before.
I understand what you say, but at the end of the day, it's just a matter of taste. To me, and after discussing that with @magopian and @davidbgk during last sprint, we feel this clean syntax is more "pythonic", and more streamlined.

Being a matter of taste, we could discuss this over and over, but as the current maintainers of AMO, we made this choice, and implemented it. If you feel very strongly about that, and wish to use the syntax you prefer, please feel free to take the ticket and implement it your way, I won't fight against it ;)