Draft: qt: unify qml type registration

C++ type registrations for the qml engine happens in MainUI::registerQMLTypes(). Singleton QML types are registered using qmldir file.

This merge request removes the qmldir files and adds commands to the function stated above for registration.

I felt it might be a better idea to deal with all registrations at the same place. qmldir files are usually used for module definition, because module is not defined in these qmldir files these singleton registrations do not bind to a URI.

It is controversial and touches a lot of files, so I'm ready to close this merge request if the changes are not wanted.