...because Alt- keybinds should be for clients to use and the A-<arrow>
default combination is a frequent user complaint because it prevents some
common usage patterns like alt-left/right in web browers.
The default `titleLayout` is updated to `icon:iconify,max,close` which
replaces the window menu button with the window icon.
When the icon file is not found or could not be loaded, the window menu
icon as before is shown.
The icon theme can be selected with `<theme><icon>`.
This commit adds libsfdo as an optional dependency. `-Dicon=disabled` can
be passsed to `meson setup` command in order to disable window icon, in
which case the window icon is always replaced with a window menu button.
There were some missing headers like <stddef.h> for `NULL`, <wayland-util.h>
for `wl_link` and <stdbool.h> for `true`/`false`.
Also this commit fixes that `labwc.h` and `ime.h` included each other.
