Support mapping of `CurrentTransformer` and `PotentialTransformer` CIM elements

[JakobVogelsang]

Acc. to the mapping document this piece of functionality is able to convert CIM CurrentTransformer and PotentialTransformer to the SCL ConductingEquipment of typeCTR and VTR, respectively.

Requirement

• make sure CurrentTransformer and PotentialTransformer are mapped to SCL

Testfile

• tbd