Talk to social_source using postMessage
remove utils/pubsub.js.coffee
disable dropbox tab by default
fix "can't select same file twice"
Merge pull request #80 from uploadcare/talk-to-social-source-using-post-message

Talk to social_source using postMessage
Merge branch 'master' into log-server-errors

* master:
  fix "can't select same file twice"
  disable dropbox tab by default
merge master -> log-server-errors