Merged requested to merge feature/move-comps-to-namespace-components into master
the constant component is already in the
Components namespace. It makes sense similar to the namespace
FluidSystems, especially as there might be even nameclashes between classes in
FluidSystems, e.g. there might be in the future a fluid system
Air consisting of components N2, O2, CO2, Ar, conflicting with the (pseudo-)component
Fixes #375 (closed).