If Dolphin crashes, changes that have been made to settings are often
lost. This has been a minor annoyance for me when developing, but it has
become a much bigger issue recently due to the problem where Dolphin
freezes on shutdown for ROG Ally users.
Instead of saving the config when certain arbitrary settings are
changed, let's save the config when the user closes the settings window.
SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
