port about-distro to qml

looks neater and also unblocks using this on mobile (though I suspect it
still needs some adjustment for the use case later)

thanks to earlier refactoring this is actually fairly straight forward
as the entry data was largely detached from UI concerns already.

- Entry is now a QObject so it can be easily passed to qml and used
there
- the kcm is now called kcm_about-distro in order to align with other
modules and have consistent naming in cmake, cpp, and the kpackage
- the main module class has grown q_properties to pass all data into qml
- the qtquick ui largely replicates the previous widgets ui. the core
distro data is fetched manually, meanwhile all entries are repeater
modeled out of Entry lists