TreeEditor can't update aesthetics

There is currently no way for the tree editor to easily update the aesthetics (colors, tooltips, etc.) and even updating the icons can be finicky. Some of this is because of the limitations of the Wx TreeCtrl and that on the Qt side we are using a `QTreeWidget` rather than a `QTreeView`.

It would be good to have a way to provide hooks that allow dynamic updating of these properties. Alternatively, a re-architecting to use `QTreeView` and `WxDataViewCtrl` so that things can just be delegated straight through might be in order.