Using LESS for CSS preprocessing.

This raises some questions about our dependencies, specifically:

* We depend on webassets==0.10.dev because 0.9 does not support
  `LESS_PATHS` which is used for easy integration with bootstrap.
* How should we deal with `bower_components` and the overall static
  situation (asset pipeline)?

I don't have a good answer for the second point right now. It really
comes down a bit to how deployment should be done in a good way.
I would very much like to have the app contain nothing but sources that
get built, or something like that.

TODO Look into instance_folders for static output?
For now, ignore bower_components