Should we deprecate changed config options?

[kosack]

In #2520, I changed a bunch of config option names, which will break existing config files. Maybe before release the next version we should add back in the old options, but with a deprecation warning? (e.g. put them back in, but with an @observe function that issues a more useful error like:

The config option write_images is now write_dl1_images, please update your configuration file

Would this be useful? Or just confusing? It could even simply forward those options to the new version, so old config files would work, but with a warning until the next release.