Improve the "as_networkx()" method

[BDonnot]

It could benefit a bit of optimization to make it faster.

In the nodes attributes, we could add different type of information such as:

• the substation to which this node belong
• the id (1 or 2) of the busbar it represents
• add some attributes such as the gen_max_ramp_up for example

And for the edges:

• the id(s) of the lines it represents
• labelling which powerline or (or ex) is the "or" of this edges
• better identifying the number of power the edge represents
• clean some of the attributes (cooldown = max of cooldown, and rethink all the others, if that make sense)