Appcontroller.m: add method refreshCurrentMessage to refetch the current
message from Cix. (menu option Message->Refresh_Message to be added in 
next commit)
Refresh Message menu item: add the prototype of the method to 
AppController.h (xcode3 wants this, xcode5 doesn't care). Add the menu
item to mainMenu.xib.
Disable the new Refresh_Message menu item where appropiate 
(AppController.m)