appdata: Improve appdata for AppStream 1.0

• Add the <developer><name> tag
• Mark the <developer_name> tag as deprecated
• Use appstreamcli to validate appdata
• Move two URLs to beneath the others
• Update the donation URL to the destination URL
• Fix release description warnings
• Remove one of Purism tag to pass appstreamcli validation

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This MR pickups where !148 (closed) left.

The metainfo file passes

flatpak run --command=flatpak-builder-lint org.flatpak.Builder appstream org.gnome.Weather.appdata.xml.in.in

after replacing @app_id@ with an actual id.