gnu: Separate Python core packages from the rest.

gnu: Separate Python core packages from the rest.

* gnu/packages/python.scm: Move hundreds of package definitions from here...
* gnu/packages/python-xyz.scm: ...to this new module.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* gnu/packages/ada.scm,
gnu/packages/admin.scm,
gnu/packages/android.scm,
gnu/packages/audio.scm,
gnu/packages/backup.scm,
gnu/packages/benchmark.scm,
gnu/packages/bioinformatics.scm,
gnu/packages/bittorrent.scm,
gnu/packages/calendar.scm,
gnu/packages/check.scm,
gnu/packages/chemistry.scm,
gnu/packages/cluster.scm,
gnu/packages/compression.scm,
gnu/packages/connman.scm,
gnu/packages/crypto.scm,
gnu/packages/cups.scm,
gnu/packages/databases.scm,
gnu/packages/dav.scm,
gnu/packages/direct-connect.scm,
gnu/packages/disk.scm,
gnu/packages/django.scm,
gnu/packages/dlang.scm,
gnu/packages/docker.scm,
gnu/packages/ebook.scm,
gnu/packages/elf.scm,
gnu/packages/emacs.scm,
gnu/packages/emulators.scm,
gnu/packages/engineering.scm,
gnu/packages/enlightenment.scm,
gnu/packages/finance.scm,
gnu/packages/fltk.scm,
gnu/packages/fontutils.scm,
gnu/packages/freedesktop.scm,
gnu/packages/game-development.scm,
gnu/packages/games.scm,
gnu/packages/geo.scm,
gnu/packages/gl.scm,
gnu/packages/glib.scm,
gnu/packages/gnome.scm,
gnu/packages/gnupg.scm,
gnu/packages/gnuzilla.scm,
gnu/packages/graph.scm,
gnu/packages/graphics.scm,
gnu/packages/graphviz.scm,
gnu/packages/gtk.scm,
gnu/packages/ham-radio.scm,
gnu/packages/image-processing.scm,
gnu/packages/image-viewers.scm,
gnu/packages/image.scm,
gnu/packages/irc.scm,
gnu/packages/jrnl.scm,
gnu/packages/julia.scm,
gnu/packages/kde-frameworks.scm,
gnu/packages/key-mon.scm,
gnu/packages/libffi.scm,
gnu/packages/libreoffice.scm,
gnu/packages/libusb.scm,
gnu/packages/lirc.scm,
gnu/packages/logging.scm,
gnu/packages/machine-learning.scm,
gnu/packages/mail.scm,
gnu/packages/mate.scm,
gnu/packages/maths.scm,
gnu/packages/medical.scm,
gnu/packages/messaging.scm,
gnu/packages/monitoring.scm,
gnu/packages/mp3.scm,
gnu/packages/mpd.scm,
gnu/packages/music.scm,
gnu/packages/networking.scm,
gnu/packages/nutrition.scm,
gnu/packages/openldap.scm,
gnu/packages/openstack.scm,
gnu/packages/package-management.scm,
gnu/packages/password-utils.scm,
gnu/packages/patchutils.scm,
gnu/packages/pdf.scm,
gnu/packages/photo.scm,
gnu/packages/polkit.scm,
gnu/packages/protobuf.scm,
gnu/packages/python-crypto.scm,
gnu/packages/python-web.scm,
gnu/packages/qt.scm,
gnu/packages/rdf.scm,
gnu/packages/ruby.scm,
gnu/packages/search.scm,
gnu/packages/selinux.scm,
gnu/packages/serialization.scm,
gnu/packages/shells.scm,
gnu/packages/simulation.scm,
gnu/packages/ssh.scm,
gnu/packages/statistics.scm,
gnu/packages/storage.scm,
gnu/packages/sync.scm,
gnu/packages/terminals.scm,
gnu/packages/textutils.scm,
gnu/packages/time.scm,
gnu/packages/tls.scm,
gnu/packages/tor.scm,
gnu/packages/tryton.scm,
gnu/packages/version-control.scm,
gnu/packages/video.scm,
gnu/packages/virtualization.scm,
gnu/packages/vpn.scm,
gnu/packages/web-browsers.scm,
gnu/packages/web.scm,
gnu/packages/wicd.scm,
gnu/packages/xdisorg.scm,
gnu/packages/xorg.scm: Update module references.