Inner nodes are painted as soon as they are added, not when the state changes.
Focus Actions are disabled (in case any of them are enabled) when clearing all annotations.
Remove outdated icons.
When adding holes to a polygon, adding a node within (clicking) its inner boundaries
is now possible.
move getter out of slots section
remove unused methods
bail out early if childObject == nullptr
return invalid QModelIndex if parentObject == nullptr
use parent class' implementation of hasChildren()
const'ify
Q_ASSERT rather than return invalid QModelIndex
checkParenting()