This is needed to access widgets to make the shell adaptive.
This also adds libhandy as a submodule and will make use of that version
if it isn't available otherwise.
In order to share the libgd and gvc modules between autotools and
meson, this patch moves their directories to subprojects
directory and updates autotools.
https://bugzilla.gnome.org/show_bug.cgi?id=785414
