Appdata related patches

data: Update desktop file

• Remove translator comment from Icon, Categories and Purism entries

This tags and comments are not visible in the pot file: https://l10n.gnome.org/POT/fragments.main/fragments.main.pot

• Add a comment for the 'Name' entry.

This tag and the comment is not visible in the pot file.

• Add new categories: FileTransfer and P2P

More information: https://specifications.freedesktop.org/menu-spec/latest/apas02.html

appdata: Update appdata

• Mark the developer_name as untranslatable
• Add categories and keywords
• Remove the first Purism tag to validate the appdata file

More information about categories: https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-categories

appdata: Use appstreamcli for appdata validation

appstream-util is obsoleted by appstreamcli.