It turns out the fastest way to update wxDataViewCtrl is to nuke the
model and rebuild it from scratch rather than via
ItemAdded()/ItemDeleted() update notifications.
Fixes: lp:1734773
* https://bugs.launchpad.net/kicad/+bug/1734773
Tree nodes now have an additional field 'InTree' to determine
if the view is aware of its existence. This way, there is no need
to rebuild the data structures from scratch when they need to be
filtered.
Maciej Suminski