Only new SoundcloudActivity records will be created

I had to get rid of the ActiveRecord callback because rails was checking
the raw soundcloud track id against the full html embed string we were
saving in the database.
Save twitter screen name from omniauth hash

This is a pretty temporary solution but twitter seems like a lower
priority at the moment and I'm not sure what kind of time investment it
is to store and use oauth tokens safely.
Twitter activity is dynamically inserted into activities/index.hbs

There is a concern here with the raw html and using handlebars {{{}}},
The right solution is to create a custom handlebars helper using
SafeString.
Fix soundcloud_jobs_spec.rb
Remove commented code from twitter_api.rb
Add twitter api background worker
Invoke twitter worker from sessions controller
Merge pull request #21 from wfro/twitter-worker

Twitter worker
merge with upstream master