Hold a map of index to `StateData` in `SuccessFullPowerFlowResult`

[sebastian-peter]

Instead of an array, use a map from index to StateData here for faster access.

powerflow/src/main/scala/edu/ie3/powerflow/model/PowerFlowResult.scala

Lines 17 to 19 in cbc20bb

	sealed trait SuccessFullPowerFlowResult extends PowerFlowResult {
	val nodeData: Array[StateData]
	}

As mentioned by @t-ober here:
ie3-institute/simona#25 (comment)