Provide search engine icons

Between 115 and 128, Mozilla changed a lot in the search engines.

I restored more or less a configuration, but it doesn't include icons, and we have warnings in the console about them.

We find some icon files and associate them to the search engines.

While doing that, we could also clean up the search engine patch and move the configuration to a different JSON file, where we add all the details we need, not only the icons.