forgot to remove previous release data

using gtk revealers for both :D

Remove build artifacts and temporary files

See merge request !2

flatpak: Use public repo URLs

See merge request !1

flatpak: Drop the old Flatpak manifest

See merge request !3

Drop the avi.wad.Organizer.json Flatpak manifest as it has been replaced
and doesn't work anyway as the application uses the
org.librehunt.Organizer reverse domain name.

Also ignore the build_ directory to avoid adding it back by accident.

add Tobias's name

upgrade to new icon created by me and @bertob

as this is only for development, and stable builds are on flathub, I can use the master runtime

add flathub badge to readme, and update version number (as FlatHub json will be updated to newer libhandy

disable unneccessary building of tests, examples, and vapi for libhandy and remove useless xdg references when home is already requested