This formats all copyright comments according to SPDX formatting guidelines.
Additionally, this resolves the remaining GPLv2 only licensed files by relicensing them to GPLv2.0-or-later.
This tab of the settings is already extremely bloated and the setting itself is quite useless.
With a gamelist of almost 30 games, the cache directory is smaller than 1MB for me and therefore I don't see why it needs to be configurable.