gnu: gnome-calendar: Update to 3.26.1.

* gnu/packages/gnome.scm (gnome-calendar): Update to 3.26.1.
[build-system]: Move to meson-build-system.
[arguments]: Enable gtk+ for meson-build-system, disable tests.
[native-inputs]: Add gettext, gtk+-bin and glib-bin, remove intltool.
[inputs]: Remove bdb and desktop-file-utils.
[description]: Rephrase and add week view.

Signed-off-by: Kei Kebreau <kkebreau@posteo.net>