Use tags to make maintenance easier

We have had a tags taxonomy (https://linuxphoneapps.org/tags/) for a bit now, so let's make it useful

• Add "No Appstream Metadata (manual maintenance)" to all apps with extra.appstream_xml_url = ""
• add feature to lpa_helper.html that takes care of this for new apps
• Add "not packaged yet" for apps not packaged according to repology, flathub, snapcraft, or notice"
• add feature to lpa_helper.html that takes care of this for new apps
• Add GNOME Circle Tag to all GNOME Circle Apps (goal: URL maintenance)
• Similar feature for apps listed on apps.kde.org