Composable OpenCV heroku buildpack

Copy pasted vulcan build from Labgoo: https://bitbucket.org/labgoo/heroku-buildpack-nodejs-with-opencv

Also copy pasted from @rumblelabs: https://github.com/rumblelabs/heroku-buildpack-cairo

Should at least work with heroku-buildpack-nodejs + the after_compile fork of heroku-buildpack-multi by salsify: https://github.com/salsify/heroku-buildpack-multi

Have fun!