add rev:css and replace:css
add rev:css and replace:css

rev:css appends the git hash to the file name
replace:css replaces the reference to the css file with the hash in the head.jade template.

todo:
  - integrate into preview workflow
  - integrate into build workflow
  - rev and replace `.js` assets as well

pupil-labs/pupil-labs-website,pupil-labs/pupil-labs-website,pupil-labs/pupil-labs-website