Replace libntxm play routine with ft2play port

[asiekierka]

https://github.com/8bitbubsy/ft2play/blob/main/pmplay.c

The license is compatible with what we distribute libntxm under, but will require packaging an extra copyright notice.

This should allow us to support most effects and FT2-specific quirks without worrying about edge cases that tracks might rely on.

0.7.0+ only

[asiekierka]

Essentially done; some things need fixing:

• Sample preview does not work unless a song was played at least once. I'm probably not setting some variable right.
• The quick fade out logic (~10ms of fade out for each turned off sample) that prevents popping is not implemented. It needs to be reimplemented while not disturbing the ft2play code port too much.
• The mute/solo logic is a hack and needs to be reworked.