Installing the headers of libplasmapotdprovidercore in the include namespace
plasma/potdprovider
as well as some CMake Config files of the name
PlasmaPotdProvider
allows it 3rd-party to develop own potd provider plugins without having
to mess with the complete kdeplasma-addons repo.

A potd-provider plugin template in kapptemplate format should speed up
development of new plugins some more.

Generated a new plugin from the template, built and installed it, selected
it in the POTD wallpaper and got the KDE logo as fetched from techbase
shown.