* Add include path of own header files for build
and external use via imported target. Previously
only include dirs required for external libs were
added.
* Using global include dirs is no longer required.
* When PUBLIC_SHARED_INCLUDE_DIRS is empty, adding
"${PUBLIC_SHARED_INCLUDE_DIRS}" to public include dirs
does not leave INTERFACE_INCLUDE_DIRECTORIES property
empty. Instead the source dir is added. So just don't
use quotes here.