Use libsass and colour adjustments

- use libsass instead of ruby sass (takes 3s to compile on my machine)
- use the `through` option in the sass loop to get slightly fuller colour coverage
- adds a `grunt sass:queries` option
- uses `$minimum-width` in the `min-width` media query
- minify css (saves about 1mb)

![img_5380](https://cloud.githubusercontent.com/assets/867233/4603460/40ed39c8-516b-11e4-88bc-e6ede3817381.jpeg)