... freeing 15 files from the big strongly connected component:
ImportFFmpeg & ODDecodeFFMpegTask (still in a cycle of two)
ImportFLAC
ImportGStreamer
ImportLOF
ImportMIDI
ImportMP3
ImportOGG
ImportPCM
ImportQT
ProjectFileManager
ProjectFSCK
ProjectManager
ProjectSelectionManager
ODDecodeFlacTask
And eight header files in src/import are deleted.
This breaks a lot of cycles because Import, which is still in the big component,
no longer includes ImportLOF, which recursively uses ProjectManager. A
registration system for the subclasses of ImportFileHandle allows that
recursion without the cyclic compilation dependencies.