Return type Try for NewtonRaphsonPF#calculate

[ckittl]

powerflow/src/main/scala/edu/ie3/powerflow/NewtonRaphsonPF.scala

Lines 95 to 98 in 63ab0e2

	def calculate(
	operationPointUnordered: Array[PresetData],
	initData: Option[StartData] = None
	): PowerFlowResult = {

Currently, only a PowerFlowResult is given back. However, if something unexpected does occur and an exception happens, this is not covered and the calling code crashes directly.