This adds a window hint string for the xdg_toplevel::app_id, which is
used by desktop environments to connect windows with application icons
and other information. This is similar to the WM_CLASS property on X11.
A few very minor fixes were done by @elmindreda during merge.
Fixes#2121Closes#2122
master
Michael Penningtonago%!(EXTRA string=3 years)committed byCamilla Löwy