Allow lessc to search for less file imports in app static folders

I've made changes which will add the `static` dir of each app into the lessc search path. You can now have '@import "abc.less";' in your less file, where abc.less exists in a different Django app. 

This means you don't have to have all of your less files under one folder anymore.

I made this pull request to your fork as I'm using both the functionality elijahr added and that I've created (i.e. my base less file is in an app, and i want it to import less files from other apps)