DSD demod fixes
Use DSDcc v1.8.6 that fixes issues when switching from 2.4 to 4.8 kBaud rate back and forth. This caused segmentation fault and it could not sync to a new mode supported by the new baud rate. This should fix #406
Other changes and fixes
- GLSpectrum and GLScope: fixed possible issues with mutex handling
- Channel Analyzer: use FFTW engine with Hamming window for auto correlation
- Use a simplified version of sample FIFOs in the threaded baseband sample sink. This is a fairly fundamental change and although the code is much simpler no significant improvement in performance was noticed.