Experimental demodulator preprocessor thread

Demodulator becoming a CPU hotspot, trying to break up the workload
between threads..
Demodulator split
Rebalance demodulator threads, tweak priorities
Font preloader, new demod no-move drag fix
Merge pull request #16 from cjcliffe/more-demod-threads-less-work-per-thread

Split up demodulator workload, tweaked OSX threads