[Matpower] Support for bus_name and genfuel optional fields

[sylvlecl]

• Do you want to request a feature or report a bug?

Feature.

• What is the current behavior?

Bus names and energy source of generators are not imported.

• What is the expected behavior?

Matpower import could support standard optional fields "mpc.bus_name" and "mpc.gen_fuel".

See for example https://matpower.org/docs/ref/matpower7.1/most/lib/t/c118swf.html . Bus names do not seem to be unique, so they still cannot be used as identifiers.

• What is the motivation / use case for changing the behavior?

Base some processing on generator type, on matpower imported data.

[geofjamg]

mpc.bus_name support is added in #2130