UnifiedEmail: Display the confirm dialog before forward.

 - Display the confirm dialog before forward one mail if the user enable
   "Confirm before forward" function.
 - The user could choose "send after loaded" or "drop the attachments".
 - If the account support smart forward, it will not show this dialog.

Change-Id: I4af283e05214e691fcb16a9351480126aee93bba