Further tweaks to DataBundle, Attribute Connector Read

Saving going well, with full details being saved. Reading has caused
problems with node not being set for the constraintItem on the superNode
read. This is fixed for Ellipses at least, should be good for all.

AttributeConnectors now load properly by updating the
AttributeConnectorsX/Y and then the AttributeConnectors List. Consider
replacing this list, since it is a little clumsy, and I cannot see more
attibuteConnectors being needed per DataBundle

Carry on testing differnt conditions with different Rigs. E.g.
constraintItems on WireGroups. Skinned Pins, and merged Nodes could all
still be problematic