Add toString on Configuration

[mbastian]

To facilitate debugging

[mbastian]

That's what we had on the processor wrapper:

return "GraphConfigurationWrapper{" + "nodeIdType=" + nodeIdType + ", edgeIdType=" + edgeIdType + ", edgeLabelType=" + edgeLabelType + ", edgeWeightType=" + edgeWeightType + ", edgeWeightColumn=" + edgeWeightColumn + ", timeRepresentation=" + timeRepresentation + '}';