Port the Flatpak Manifest to YAML
Our current Flatpak manifest is in JSON, flaptak-builder supports YAML too since not too long. The format is better suited for Flatpak manifests as it is easier to read and write for humans and it supports comments.
I would recommend to wait for the release of GNOME Builder 3.30 as a stable flatpak before porting though, so bevelopers relying on the stacle Builder will still be able to compile Calls.