Better display Twitter threads

[philgyford]

At the moment Tweets are always a single list. But we should maybe look at, if we have a thread (e.g. on this daily archive page) then do something in the view that reorganises things so it can be displayed better in the template.

We should handle both:

• Where all the tweets in a thread are replies to the first tweet, and
• where all the tweets are replies the previous one in the thread

We'd maybe want to add a thread field to the Tweet we're sending to the template, that's a list of all the subsequent threaded Tweets?