We want to use the vfunc of the class to implement devices coming from a
Qemu object on D-Bus, but we don't want to expose that in public API.
Instead, we can keep the object instance and class internal but still
expose the subclasses as public API. We have to do old-style class
definitions to do that, but worth the ability to keep public API limited
so that we can make changes later.
Adds MksKeyboard and MksMouse types. Setup a MksScreenKind for the
MksScreen based on MksQemuConsole:type property. Currently the keyboard
and mouse are not wired up, but here for scoping out the properties.
