BUG: 2065601
* Show Unread Count of Accounts in AccountFolderList
* Change the background according to the folder's type
* Change the style of unread counts
TODO: Change background images of Unread Count
* Attachment icon is displayed when message.mAttachment != 0
* Favorite icon is set/cleared from message but not clickable
* Selection icon is not clickable
Further progress requires implementing a custom child view which can
handle sub-clicks properly.
* Add MessageList Activity class and Manifest entry
* Add appropriate layouts, views, etc.
* Wire into FolderMessageList
Lots to do, but this gives us a useable screen.
