Large refactoring

Biggest achievement: Decouple StatusView from Monitor

Monitor is now a QObject-based classes, emitting signals for {new,
updated} {jobs,nodes}. Monitor no longer depends on StatusView. This way
we have a better separation between model (Monitor) and view
(StatusView).

Another positive effect is that now JobListModel and
HostListModel are completely independent of StatusView, too. They solely
depend on a Monitor instance and keep their model up-to-date
theirselves. That enables us to write views that depend on an
QAIM only without any extra code.

You may have guessed: I'm thinking about a QtQuick-based UI
here!

Note: Didn't port PoolView. In fact, I'm thinking about dropping it
altogether.
Extend FakeMonitor