Adds musicpref to console and sound options menu, which allows users to select whether to prioritize MIDI or Digital music.
Functions GameMIDIMusic_OnChange and GameDigiMusic_OnChange updated to not assume digital music priority, and to have more consistent behavior between the two.
Positive side effect of using P_RestoreMusic in these functions means that powerup music (speed shoes, invincibility) will restore in the correct position when reenabling the original MusicType they loaded in with.