Add JsonConfigFile class to access JSON config files as dicts

This is what a PR looks like!  You guys should both have push rights, so you should both be able to merge this.  I've done some work in a branch, pushed it to the repo, and this is a PR to merge my work into the main branch ``master.``  I could merge it myself, and in many cases we probably will, but this is a nice way to get feedback.  You can comment on the PR in general or on specific lines.  If I add commits to the ``AddJsonConfigFileClass`` branch, they will automatically be shown here.

@burtonjb @Linus744 Please review.  Thanks.