Cleanup use of rnew, cpnew and co. from module conc_mod

[emillour]

cpnew (Cp of atmosphere), rnew (Reduced gas constant of the atmosphere) are 3D fields (if running with photochemistry and/or thermosphere) which are stored in module conc_mod.F90

They are recomputed every time step via a call by physiq to concentrations.F (or set to constant values by physiq if running without chemistry and/or thermosphere).
However cpnew, rnew, etc. are set/accessed in various routines via "use conc_mod ..." statements rather than as arguments to the routines that use (or modify) them, which makes the code hard to follow and understand.

A good cleanup, where these variables are sent to routines as arguments and not accessed via the conc_mod module would improve code readability.

Work done in r3185 and r3186.