This ensures that:
- Plugins are only used once,
- Group names are unique,
- Lines match: group = plugin[, plugin[, plugin ...]],
- There are some groups and plugins defined,
- The plugins used are installed.
Previously, we hardcoded a list of icons for Atto plugins. This is not
a good idea as it would be very quickly outdated, or incomplete. Now,
we proceed as we often do: if the image pix/icon exists in the plugin
it is displayed, else nothing is displayed.
Marina Glancy