Feature/12 trello integration

WIP
@Nowaker @DragosIorgulescu @trbritt 
Thought I'd ping you on this one.  I'd just like some input on this technique to pass an OAuth2 token to the browser.  
I've researched it and it seems fine since:  Client-side apps use OAuth keys quite commonly.

Clearly, this will require SSL.

There are some significant advantages to doing things this way:

* It lets us make API calls directly through the browser, instead of tying up the server with brokering the request on behalf of the client.  These can be done in parallel and with the benefit of the browser's HTTP cache.  The Kanban board is significantly faster loading the issues than the dashboard because of this.

* There is no need to divulge the client secret to the browser session, as the OAuth request is brokered through the server.

The obvious attack is XSS, but if the server is brokering requests from the browser, it'd be technically possible to exploit that with XSS as well.