Add DTMF handling for '*' (repeat menu) and '#' (return to menu/exit)

Adds support for the following DTMF buttons:

'*' - repeats the last menu.
'#' - exits from the change folders prompt. If already in the main menu, plays bye and hangs up.
Since a lot of this is repeated from the current code that plays the menu, I would move most of this into a method attached to the finite state machine. Would not be a bad idea to have a method return the prompt necessary to play the menu since in this instance, there is no need to transition to the 'ready' state. getMenu is already attached to the finite state machine, the code to fetch the sounds from the config and perform the replacements and create the prompt could be moved in there.