Enh: updating an installation - how to update local config files

There are several files which need to be configured for each local installation.
- site/js/config.js
- site/api/lib/config.lua
- tools/ponymail.cfg

These are not included in a release, but are created as necessary by setup.py.

If an updated version is to be installed over an existing installation, that works fine so long as the new release does not require changes or additions to the files.

The release notes for a new release should detail any changes, but it would be good if changes could be handled automatically by some config upgrade process. Or perhaps there could be a config checking script which warns of any missing or obsolete settings?

Start with setup.py and the local configuration files site/js/config.js, site/api/lib/config.lua, and tools/ponymail.cfg. Determine whether the work should automate configuration upgrades or provide a checker for missing and obsolete settings; done means the chosen process handles configuration changes during an update or clearly warns about them.

Written by the indexing model from the issue text.