Add an 'untrash' action

My mail setup involves IMAP clients that seem to love to set the 'trashed' flag on messages. These are irritating, so I added 'untrash', which is simply 'unflag' that removes the 'trashed' flag. I used the = key for the usual no good reason. 

I'm not in any way married to this approach; if my IMAP server and various other clients worked better, it wouldn't even be necessary.