Fix MIDI so it's reliable

Microsoft in Windows 10 (and I think Windows 8) moved "MIDI Mapper" support from the control panel  to the program.

We urgently need EW6 to be able to set the Midi Output channel for MIDI tunes we attach to Hymns.

EW6 needs to be able to set & store the selected MIDI output device and then set it every time it starts up.

FYI: The "Vista Midi fix" as shown in the forums is very hit and miss.