Maintenance release
- Fix map feature 5.15.4 check. PR #1370
- M17 library some code rework
- DATV demod: allocate DATVDemodSink dynamically
- New threading model for some plugins: DSD demod, NFM demod, SSB demod, FileSink, SigMFFileSink
- DSD demod GUI: fixes for non existent AMBE feature. Fixes #1334
- Corrected order of deletion of feature vs feature GUI. Fixes #1332
- Some OpenGL fixes. Issues #1351 #1359. PR #1361
Note Ubuntu 20.04 build removed due to abuse.