editor: Cleanup and improve styling (GTK4 papercuts)
- Use a single class for "main widgets" of a property editor and use widget names to specify further (eg. don't create a "main-entry" class but use entry.main-widget instead). This helps in keeping things consistent
- Fixup some margins and paddings. For example, the birthday row doesn't look smaller than the rest anymore.
- Use the margins to vertically align icons iso centering them
- Fix a warning when setting an address