Optimisations

[keithamoss]

• Use a shouldComponentUpdate OR a tweet selector on UserReviewQueueViewContainer and TweetColumnContainer so that they only update when the assignments/column change (which hold the ids of the tweets), not when any tweet object changes
• Ensure heavy parts of the UI (e.g. triage view) only update when absolutely necessary
• Reduce what gets passed down to TweetColumn as much as possible (e.g. Does it actually need the details of assignments or just that there's a tweet_assignment?
• Take a quick pass over TweetColumn and look for performance improvements
• Does switching to queue and back to columns maintain scroll position in each column?
• How does triage actually know when new tweets are being added above your position in the list?
• Can we intelligently discard tweets for users not doing triage (i.e. They only need to have tweets stored locally that are assigned to them or that are enough to load TweetColumn)
• Maybe we don't need to send users new tweets and store them unless they're on triage view and the tweets are within X of their current view?
• Maybe we can only send tweet data if it's part of an assignment. For triage just send a new tweet total.
• Does loadMoreRows work for future tweets (scrolling up)? How does it now that tweets are being added at the top and not elsewhere?