Merge branch 'libknot-unified' into 'master'

libknot unified

This MR removes extra shared libknot-* libraries from distribution.

There are now only three libraries visible to the public:
libknot
libdnssec
libzscanner

Due to the cross-use of libknot-internal from libknotd and libknotus, some code might be linked twice, but it's inevitable unless we want to expose volatile API/ABI to the outside world.

The few more things:
- Removed all _public_ declarations from internal/* and yparser/*
- Add #include libknot/internal/macros.h to internal/* and yparser/* (as a side effect from playing with symbol visibility)
- Fixed library versioning and bumped libknot from SOVERSION 0 to 1, since some symbols have disappered since (due to visibility)

See merge request !379