Update Desktop Entry and AppStream metadata files

[Vulcalien]

I updated the .desktop and .metainfo.xml files, fixing a typo (pplication/x-agb-rom), adding the new releases to the changelog etc

I also changed the project license from GPL-3.0 to GPL-3.0+ (tell me if I'm wrong, I think NBA is GPL 3 or any later version).

[fleroviux]

I also changed the project license from GPL-3.0 to GPL-3.0+ (tell me if I'm wrong, I think NBA is GPL 3 or any later version).

That's correct yes

[Vulcalien]

I updated the files to the latest version in the flathub submission. I don't think they'll change anymore soon.

[fleroviux]

@Vulcalien Thanks for your efforts. Should I go ahead and merge this already?

[Vulcalien]

Should I go ahead and merge this already?

Yep, I'm done with these changes