#39 Midi input/output selection

This was BUG: 911223
Reported by: Patrick McFarland - diablo-d3

Currently, ssm only allows you to set the oss midi device
you want to input and output midi to. When ssm is using
alsa midi, this option is still displayed, but is completely
useless as alsa doesnt use that.

I think ssm needs a method to allow the option dialog to
either change what settings it displays for midi (oss
devices for oss, alsa connections for alsa), or even
remove it from the options dialog and make the option
apart of the midi plugin itself.

This would make it easier to use ssm, and make it less
confusing for newbies who dont know the option doesnt
do anything when alsa midi is in use.