feature complete twitter app clone

[adamtait]

here's my complete twitter app. I spend quite a bit more time with this one than previous apps and I think it really paid off. I'm mostly happy with the results and I know I'm way more comfortable with layouts & constraints than I was before. In hindsight, I could have used interface builder more (I only have 2 xib's), but layouts without interface builder have their benefits, too (see my ADRs).

Additions I'd still like to make:

• The missing killer feature really is the clickable links. I use twitter mostly as a news source and without clickable links, I can't do that.
• Network errors could be handled better. The app should sign out the user, and notify them. At the very least, favorites & retweets should not appear active.
• on pull to refresh, I'm reloading all the tweets. This is both slow and destroys the cache of the tweets that have built up from infinite scrolling.

/cc @nesquena @timothy1ee