Recent versions of Gettext are able to translate several formats
that are used in GNOME applications. This patch migrates from
Intltool to Gettext by using meson's i18n features.
https://bugzilla.gnome.org/show_bug.cgi?id=787588
gettext can extract strings from xml file formats with the help of
.its files. Provide appropriate rules so modules that install
keybinding descriptions don't need to depend on intltool to
extract translatable strings.
https://bugzilla.gnome.org/show_bug.cgi?id=769066