implement the "console startgui" and "console stopgui"

implement the "console startgui" and "console stopgui"
commands so you can start and stop the gui even outside
of a call. This is convenient for testing, and also for
using the keypad to pick up a call, and to dial a number
(the latter not yet implemented, but should be close).

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@97390 65c4cc65-6c06-0410-ace0-fbb531ad65f3