add all object properties to node

[danielpcampagna]

I needed to access the property style of the xml object in the node, but the node just had the properties id and label (with the value of property value?!). So I've added this lines so the node have all xml object properties.

Example:

Before this PR, we had:

>>> diagram.edges_ids
{'NYdg3bHRsR49v2e3w9m-': ['FRgOEqRr26YJtNhKciwV-1']}
>>> diagram.current_root[-3].items()
[('id', 'FRgOEqRr26YJtNhKciwV-1')]

With this PR, we have:

>>> diagram.current_root[-3].items()
[('id', 'FRgOEqRr26YJtNhKciwV-1'), ('style', 'rounded=0;orthogonalLoop=1;jettySize=auto;html=1;opacity=20;endArrow=none;endFill=0;jumpStyle=gap;'), ('edge', '1'), ('parent', '1'), ('source', 'FRgOEqRr26YJtNhKciwV-21'), ('target', 'FRgOEqRr26YJtNhKciwV-2')]