Removes artificial limit in artist picker traversal. There are quite a
few object (fig, VPacker, etc.) which do not contain an axes property
and would not be traversed for picking logic without this change.
Reverted the children picker traversal back and added extra check so
that children are picked if the current object does not have an axes
property.
Merge pull request #2756 from cimarronm/remove_picker_limitation

Removes artificial limit in artist picker traversal. There are quite a