Issue #1054: Improving comment like Notification UI

1. Added a couple Helper-Model-Objects, so we can concentrate parsing logic in just one spot:
  * **NoteBodyItem**
  * **NoteAction**
2. Added **WPTableHeaderViewCell** helper class.
3. Re-written **NotificationsFollowDetailViewController** to rely entirely on UITableView. 
4. Added a couple new styles in **WPStyleGuide** helper class.

Suggestions / Change requests will be very welcome!