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

shift from GtkStackSidebar to ListBox, now hiding the categories of files not found, and showing the first proper one!

get label for file categories, for mobile users to know what file category are they in (and it looks good)