Improve Linux builds (#343)

* Improve Linux builds

- Add .svg redraw of png icon
- Add FreeDesktop metainfo.xml catalog info for package managers
- Change FreeDesktop app ID to org.fteqw.fteqw as fteqw.org seems more up to date than triptohell.info
- Have cmake install deploy these to appropriate locations
- Update Flatpak build manifest to modern yaml standard
- Include optional dependencies in Flatpak (except libcef which fails to build and I cannot figure out why)
- Add launcher script for the Flatpak that checks and warns about game data
- Add some patches to make the Flatpak builds work better
- Add Flatpak builds to CI

* Fix missing end-of-file newline

* Fix repo url for fteqw