(issue1801) Unify reference gauge finding code The basic way as described in the method comment of the determineRefGauge method is now used in the WINFOArtifact, MainValuesService and RiverUtils.getGauge method. RiverUtils.getGauge previously just returned the first gauge found. While this is now a behavior change I believe that it is always more correct then the undeterministic behavior of the previous implmenentation.

- Validation of the input values of an incoming feed() call