server-side sorted comments

[roadscape]

The backend discussion API is being updated to accept a sort parameter. Condenser needs to stop sorting comments client-side and instead pass the sort param to the backend. The only difference of the response is that the replies key of each comment will be pre-sorted.

When changing comment sort order in the UI, condenser will need to issue a new request, and re-render the tree. The signature of the call is bridge.get_discussion(author, permlink, sort).