Mixer: Implement basic groups.
Mixer: Add group DSP meters.
Set FTZ and DAZ flags by default for all JACK client threads.
Mixer: Fix group membership of new strips.
Midi-Mapper: Close gracefully on sigterm.
NSM/JackPatch: Replace mutex in callback handling with ringbuffer (may help with JACK1 which runs the callbacks in the RT thread).
NSM/NSM Proxy: Add two new options. Stop Signal and Config File.
Tweak buffer ops for GCC auto vectorization.