Rework cmake, the original plan was to maybe be able to use conan targets with...

Rework cmake, the original plan was to maybe be able to use conan targets with the same name (that's why 3ps had names like apr::apr),
but it's safer and saner to put the LL 3ps under the ll:: prefix.
This also allows means it is possible to get rid of that bad "if( TRAGET ...) return() endif()" pattern and rather use include_guard().