appdata: Improvements for AppStream 1.0
To replicate the validation at Flathub we use:
flatpak run --command=flatpak-builder-lint org.flatpak.Builder appstream *appda*
I: io.bassi.Amberol:44: developer-name-tag-deprecated
The toplevel `developer_name` element is deprecated. Please use the `name` element in a
`developer` block instead.
I: io.bassi.Amberol:269: nonstandard-gnome-extension kudos
This tag is a GNOME-specific extension to AppStream and not part of the official specification.
Do not expect it to work in all implementations and in all software centers.
✔ Validation was successful: infos: 2, pedantic: 5
it succeeds with this MR.