Initial Twitter integration

Duplicates Instagram work, fetching tweets for designers with Twitter IDs (screen names), saving fresh findings into the database.

Munges the tweet attributes to match the names of Instagram properties, so layouts "just work".

Introduces `.env` file config for [Foreman](http://ddollar.github.io/foreman/) (or [Honcho](https://github.com/nickstenning/honcho)), `.gitignore` updated to keep this out of version control.

Main Twitter logic has commented-out methods, implementation to follow - e.g. hashtag search.

Run `npm install` to pick up [MTwitter](https://npmjs.org/package/mtwitter).