Improve cell name autocompleter implementation
Currently the advanced settings tab allocates a new QCompleter assigned to a raw pointer every time cells are changed and assigns it to "start default character" field every time available cell names are updated and data files tab sends the appropriate signal. There are two problems:
- It may assign the completer to the field when it's disabled (e.g. when skip menu check box isn't set). It doesn't seem to cause obvious problems at the moment, but my Qt release complains that apparently
Setting a QCompleter on non-editable QComboBox is not allowed.
every time the launcher is ran. This message is displayed twice even though I would expect the cells list to only be updated once when the data files page isn't touched by the user, which might be a sign of a different problem. This message is also displayed even if the field the completer is assigned to isn't actually disabled, which probably means that the completer is assigned to the field when advanced page didn't yet manage to load any settings.
- The completer probably doesn't need to be constructed again every time cells are updated.
I'm not proficient enough in Qt to figure out how to fix these issues cleanly.