Integrate Twitter feature from RGSOC
https://github.com/leapcode/leap_web/blob/develop/doc/TWITTER_FEED.md
Todo:
- create config/secrets.yml:
--- production: twitter: bearer_token: 'xyz.....' enabled: true twitter_handle: 'bitmasknet' twitter_picture: nil
(from redmine: created on 2016-09-28)