The goal here is to keep the MksPaintableListener inside of MksPaintable
so that we don't have to create API between the two. Additionally, the
MksPaintable can own it's own G-DBus connection as we don't want to share
them for updates with anything else (as they can have large data chunks
coming across).
This is ultimately going to give us back a paintable, but it's only in
partial state right now. We need to figure out the right semantics for
ownership between the listener/paintable/screen/etc.
We may want the widget to be the owner of everything (and keep the
painable/listener internal API) which is likely the most convenient from
an object ownership standpoint.
