(issue1755) Generalise BedQuality result handling The bedquality calculation now produces a result for each time period which has BedQualityResultValues for each specific result type. Formally this was split up in density, porosity and diameter classes with some bedload diameter classes mixed in for extra fun. The intent of this commit is to allow more shared code and generic access patterns to the BedQuality results.

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