FEAT(config/env): add ability to sync config vars with heroku

* add mongolab addon to heroku automatically by default on deploy
* sync config vars with heroku on initial deploy
* add documentation about mongolab addon
* make sure env var for mongolab matches heroku mongolab env var:
  now MONGOLAB_URI instead of MONGOLAB_URL
* add grunt copy for distgitignore to ignore .env and copy to copy it
  and .env to dist/