* This still isn't perfect with some custom style stuff but it's next
to impossible to get working right. In theory we should manually
draw PE_PanelItemViewItem in the gap in drawRow() or so to make sure
we also draw any on-hover highlight over objects, but that doesn't
seem to work.
* We add our own custom item model to handle the cases we need. We can
also make a few assumptions and optimisations around things we can
safely assume like e.g. nodel columns won't really change after init.
* This lets us have full control over batching updates, which was the
main motivation, but it makes it easier to extend in future (e.g.
adding single per-item tags instead of the heavyweight Qt::UserRole
data elements).
baldurk