Convert CGMES to IIDM node-breaker topology

[zamarrenolm]

Currently all CGMES models are mapped to IIDM at bus-breaker level.

CGMES node-breaker models must be mapped to IIDM node-breaker level.

CGMES bus-branch models could be mapped to IIDM node-breaker (they could contain retained switches) or directly to bus-breaker. Consider if this should be configurable by the user.

In PowSyBl it is important to leave the bus-breaker level available, because it could be used in some analysis functions.

[zamarrenolm]

When mapping to IIDM node-breaker we should set the retained flag of switches. If we keep this information we can use the Topology Tester, that compares the topology given in the CGMES TP subset with the topology calculated by PowSyBl.

The topology is also comparable if CGMES model is mapped to bus-breaker level but there are no retained switches (the switch adder of bus-breaker view in IIDM does not allow to set the retained flag for the switch).