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.
I'm not sure it's a good idea to overload the change folder submission process with this. I think it would be best to change the regex in the config.json to only expect digits for this action to be called when in the 'changingFolder' state and set # and * to go to the lastOptions and resetExit (or previousMenu and repeatMenu) actions defined under the 'changingFolder' state.

This way there's an api that can be implemented (previousMenu, repeatMenu) by different states and handled appropriately.