"NetworkManagerUtils.h" contains a bunch of helper tools for core
daemon ("src/").

Unfortunately, it has dependencies to other parts of core,
such as "nm-device.h" and "nm-platform.h". Split out a part
of tools that are independent so that they can be used without
dragging in other dependencies.

"nm-core-utils.h" should only use libnm-core, "nm-logging.h"
and shared.

"NetworkManagerUtils.h" should provide all "nm-core-utils.h" and
possibly other utilities that have larger dependencies.