Define a command-line switch that silences non-essential stdout chatter, if desired

[axch]

Said chatter would be

• The progress reports called for by Ensure that progress reporting is on by default and user-friendly #13
• The start/stop notifications
• Possibly some of the warnings (not errors) detailed in Error and condition reporting strategy #45

Implementation options:

• Teach the core to accept command-line or environment-variable arguments for items like this that do not affect model output, or
• Add yet another item to the parameter file.

The Python driver program can translate its own command-line switches to whichever of these methods is chosen.