Add viewDidUnload for ExternalWebViewController to nil out IBOutlets, add webView didFailLoadWithError to stop spinner if web view load fails.
[DONTNEED] log statement to log every single webview request (for now).
Add viewDidUnload to DTCViewController to nil out outlets.
Update deployment target to iOS 6.0, add Social framework
[ADD] "Tweet Sheet" to nav bar (in storyboard), presentTweetSheet action method in TweetsViewController
[DONTNEED] commented-out code for twitter transition
reorganize/clean up logic for handling URLs from main controller
[REMOVE] "twitter_loading.html" and "graybird.png" (not needed anymore)