Migrate away from supporting theme aliases?

[neiljp]

In #612 we migrate theme names and add an alias table which allows the old names to continue working.

This issue is to track whether in future we remove this theme aliases dict - possibly in one major release first as a fatal error at loading, indicating more strongly that the theme should be replaced (or automatically updated in the file, or other location?) - and then in the next significant release actually removing the aliases and treating the old names as invalid.

[Ezio-Sarthak]

Could you elaborate about automatically updating, and potentially in which file?

[neiljp]

Automatically updating would be the source of the provided configuration; I'm wary of doing this as we're touching user config, but we're not yet at a stage where we need to consider this change. This may be less problematic after #678 if the config is separated from profiles and we generate a guaranteed new proposed config file.