ENH: Choose the transformer orientation

[benoit9126]

Describe the feature you want. What problem does it solve?
Currently, when defining a transformer parameter, a "high voltage" and a "low voltage" are defined. When using this parameter in a Transformer, the high voltage side is attached to the bus1 and the low voltage side to the bus2. It should be possible to choose the other orientation in order to increase the voltage in a network.

Describe alternatives you've considered
Another parameter should be added to the transformer constructor in order to select the "orientation of the parameters".