WARNING: multi directory commit, needed to secure it builds.
leaving the shared backend sources in core, imposes a severe limitation,
that they cannot make use of e.g. qt-models, because that is created
after core (first library to be created).
The shared backend uses functionality from core and qt-models, so it
must be created when those are available and before desktop-widgets
or mobile-widgets are created.
Make a new root directory "backend-shared" with empty CMakeLists.txt
Signed-off-by: Jan Iversen <jan@casacondor.com>
