Also:
- use consistently term "profile" instead of "group"
- mark default profile with suffix "(default profile)" in combobox list
- make buttons for editing profiles icon-only, similar to other places with buttons in one row with the combobox (avoids also size issues with translated button texts)
- splits the single model class into two separate model classes, one for list of profiles, one for variables of a profile
- makes all UI updates (like button states) follow model signals instead of direct setting