Radio: Added ConstantErrorModel.
Radio: Renamed to APSKErrorModel.
Radio: Deleted obsolete NullModulation.

Also added FlatTransmitterBase.
Radio: Fixed issues after recent refactoring.
Radio: Moved background noise models.
Radio: Moved radio parts to apsk directory.
Radio: Changed visualization to fill communication circles only when transparent.
Radio: Renamed various parts to APSK*.
Test: Followed recent renames.

Updated names in fingerprints, no other change.
Radio: Renamed background noise classes.
Test: Renamed test files according to new naming scheme.
Radio: Moved analog models to analog directory.
Radio: Renamed attenuation to *AnalogModel.
Radio: Renamed directory to analogmodel.
Radio: Renamed Flat* to Narrowband*.