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.
Switching to loadingFolder will cause the finite state machine to never get out of that state. When actually changing folder, this.messages.changeFolder transitions to intro upon success but there is no way for that to happen here.