[mythtv] Ticket #7887: Additional MusicExitAction option for MythMusic

[Garrick]

> the way to work around
> this *without* code is to simply use the exit to main menu jumppoint to
> leave MythMusic.

This is a bigger issue than just the MythMusic plugin (a remote
control has no way of knowing that MythTV is currently in the
MythMusic plugin as opposed to some other state).  The jumppoint does
not exit back to the main menu from all states of all MythTV plugins.
A series of ESCAPEs has been the only way (short of killing and
restarting the frontend) to guarantee that the MythTV frontend can be
put into an idle state from any possible state of any plugin or
activity.

The goal of the patch that I submitted is to allow users to have the
option of using the very useful "prompt on exit" functionality *and*
be able to have remote control macros that can exit from any possible
state.

-Garrick