consistent implement lower bound for density

[mimeissner]

for a more robust behaviour use lower bound for density in all components (currently used in some).

missing components: DynamicPressureInflow, DynamicPressureOutflow, JunctionN, TransportDelay, Compressor, Turbine, Fan, ThermalConvectionPipe, Nozzle, PartialValve, getQuantity(?), Undi->JunctionMN, Undi->TransportDelay, Undi->PartialValve