Simple social network handle lookup

Lookup works for several social networks – right now they're being styled with a simple placeholder border, in `app/styles/app.scss`.

Note: this PR contains commits in #3 -- we'll probably want to merge that one first.
I think Ajax callbacks need to use the [Ember run loop] 
(http://emberjs.com/guides/understanding-ember/run-loop/#toc_what-scenarios-will-require-me-to-understand-the-run-loop)