Add command line functionality

Presently there's only the GUI to run the schema parser. This is very convenient - especially because it remembers output directories and stuff.
It was originally planned that the parser could be run as a command line application with switches to set what outputs, directories and stuff.

This is still to be done.

Start by locating the existing GUI entry point for the schema parser and reviewing how it remembers output directories and selects outputs. Define the command-line switches and expected behavior for running the parser without the GUI, then document how the completed CLI should be invoked and verified.

Written by the indexing model from the issue text.