Allow add node style to use attributes set in the attr_dict

[jlaw9]

Currently, attributes set in the attr_dict of the add_node_style function will be overwritten by the default if they are not specified in the function. A way to fix this would be to have the same kind of if statements that add_node has, and if it is not None, set it to the specified value.

add_edge_style also has the same problem.

[jlaw9]

Actually, this is an easy fix. Just need to swap attr_dict.update(style_properties) to be style_properties.update(attr_dict) and then set att_dict = style_properties to overwrite the defaults with whatever is specified in attr_dict.

[jlaw9]

This is fixed.