I've attached decouple_config.patch, which removes some internal knowledge about EditorWindow from configDialog. This is a step towards making the preferences dialog non-modal (and also to launching either the current dialog, or a new ttk-dependent one).

The thing that could currently break things if we switched to non-modal is that when configuration changes, we directly examine "parent.instance_dict". Unfortunately, it's possible that parent will have been destroyed before this happens.

Instead of holding onto parent, the patch holds onto the FileList object, which should persist. It also takes the opportunity to delegate the specifics of what should happen to active editor windows on config changes (previously in configDialog) to FileList, which in turn delegates the specifics back to each EditorWindow instance.

A separate patch, depending on this refactoring, will then change the dialog so that it can be launched non-modally, and make sure only a single instance is present.