Key changing dimension, 24-bit samples, locking

Support for 24-bit samples. It just so happens that the only GIG file I
have that is 24-bit also has the key changing dimension set, so I
implemented that so I could compare the output sound with that of Linux
Sampler. It still sounds different, brighter in LMMS. Not sure if that
has to do with gain, ADSR, or incorrect 24-bit decoding. I'm guessing
ADSR.

There were many crashing issues when playing notes when changing
patches/instruments. More locking, less crashing. However, this also
means that it is quite slow when playing a lot of notes with large
samples and converting sample rates. Linux Sampler amazingly can handle
36 or so keys being pressed at once whereas LMMS nowhere near that many
at the moment.