[FR] Some settings UI improvements

[shumadrid]

I did see a recent #878 issue that already made improvements. I have some more suggestions:

1. Show invalid textbox states for invalid settings instead of sending notices (which were deleted in fix(settings): remove ability to enter non-number in number input boxes #880 PR, but in the current implementation you can still specify negative numbers)
2. Set all default settings as placeholders (even after save, by naively checking if the saved setting matches the default one, and then setting a placeholder instead of .setValue())
3. Set a 80ms delay between saving the toggle settings that enable other settings, and refreshing the display, so that the toggle doesn't jump from one state to another but looks at least a bit like the others (imperfect fix but easy)

I can submit a PR for this if the maintainer agrees.

[Vinzent03]

To your specific points:

1. I would not overengineer it, putting in negative values just makes no sense and I don't think people come up with the idea of doing it. So I would just accept that.
2. I like the idea. This allows a more visual representation of resetting to the default value than the current one with the zeros:
   
3. Yeah I noticed that issue myself already. This feels kinda hacky, but should work pretty fine.

If you want to work on a pr, that would be great!