flatpak: Run EDS nested to the sandbox

EDS keeps changing its D-Bus API and we can't really
rely on it matching the host. Thus, make EDS run nested
to the sandbox.

build-aux/flatpak/flatpak-wrapper.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+if [ "$1" = "--quit" -o "$1" = "-q" ]; then
+    /app/bin/gnome-calendar "$@"
+    exit
+fi
+
+export GIO_USE_NETWORK_MONITOR=base
+gsettings reset org.gnome.evolution-data-server network-monitor-gio-name
+/app/libexec/evolution-source-registry &
+sleep 1
+/app/libexec/evolution-addressbook-factory -r &
+/app/libexec/evolution-calendar-factory -r &
+sleep 1
+/app/bin/gnome-calendar "$@"