Support less via less.js during development

[fwenzel]

If I add some less files to a bundle and set TEMPLATE_DEBUG=True, jingo-minify should add a script tag for less.js as well, so that the less files are interpreted on the fly. This keeps me from having to install node.js and lessc and all that jazz unless I want to.

[jsocol]

This means we'd have to add less.js as a static file and, thus, staticfiles and all that, which is a pretty big conceptual change. Maybe a good one, but not easy. Or a setting like LESSJS_PATH and force downstream projects to include it.

[fwenzel]

Hm, I'd be fine with having to define it in a setting. At least this way I wouldn't have to manually add it to my templates wrapped in an if clause so it doesn't show up in production :)

[gkoberger]

We do it on zamboni, however it would be nice to make it just work right out of the box. I think it'd be fine to make projects specify the LESS location, since we already make them point to where they installed lessc.