Refactor Settings

At the moment the settings are entirely described through the enum variants and their values. However this has become quite annoying because we use different variants for the different kinds of combo boxes we have. It would be much better if we could just dynamically describe a combo box instead. This is not currently possible because the options would need to be part of the value, which means they would also be stored back when changing such a setting, which doesn't make any sense.

We should look into further improvements such as groups and tooltips while doing this refactoring.

Start by locating the settings enum variants and the code that stores changed values. Clarify how dynamic combo-box options, groups, and tooltips should be represented; done means settings can describe combo boxes without persisting their options and the requested improvements are covered.

Written by the indexing model from the issue text.