Loading animation for Twitter feed refresh

Use a UIActivityIndicator to show a loading animation in the left
UIBarButtonItem
Added source link for animated UIBarButtonItem

Original code came from the following Stack Overflow page:
http://stackoverflow.com/questions/2965737/replace-uibarbuttonitem-with-
uiactivityindicatorview
Merge branch 'animated-uibarbutton-for-twitter'
Rename special events bar button

Changed from “!” to “Events” to make it more clear what this
UIBarButtonItem does
Merge branch 'tweak-special-events'