Added do mail

I added a feature to do things.  By typing do mail it will take the first selected entry from mac mail and add it as a task with the tags email and the name of the mail box.  It also includes a link to the message in mac mail. It is a tweak based on the code found on http://www.tuaw.com/2013/02/15/friday-favorite-using-applescript-to-work-with-tasks-in-things/.