Deprecate .pcz and use plain .zip instead
Created by: akien-mga
Cloned from #2788:
How about just deprecating the .pcz extension and use zip? We can make the exporter also write zips as an option to pck.
Writing zips would be great, I've needed to create and debug my own pcks many times.
For the extension I don't mind either way, zips have many names nowadays, starting from the first Quake packages (that's actually where I found out about minizip, the library we use to read zips, the original Quake source), but also IPA, APK, etc. I suspect their reasoning is just to stop the operating system (and random users on some cases) from handling them, and to possibly associate the extension with their own program, which I'm not sure it's worth it for us.. We did have to rename the templates package for similar reasons a while ago..