JANUS workflow

[lsoucasse]

I think the JANUS module can benefit from a clearer workflow with new functions that encapsulate the main steps one can find in the SocRadConv script or the demo scripts (and the PROTEUS main script!).

It could be something like:
janus.setup_directories
janus.set_stellar_luminosity(stellar_spectral_file)
janus.run(config_file)
janus.write_atmosphere()
...

This is linked with the management of input data/parameters in both JANUS and PROTEUS (issue @FormingWorlds/PROTEUS#74)