gnu: Add GNU Freedink.

* gnu/packages/games.scm (freedink-engine, freedink-data): New
  variables.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>.

services: Add 'auto-start?' field to <service>.

* gnu/services.scm (<service>)[auto-start?]: New field.
* gnu/services/dmd.scm (dmd-configuration-file): Honor it.
* gnu/system/install.scm (cow-store-service): Add 'auto-start?' field.

gnu: libmikmod: Avoid dlopening libasound & co.

* gnu/packages/sdl.scm (libmikmod)[arguments]: New field.

doc: Mention "audio" and "video" groups in configuration template.

* gnu/system/os-config.tmpl (users): Add "audio" and "video" groups and
  explain.

services: Add 'user-unmount-service' as an essential service.

* gnu/services/base.scm (user-unmount-service): New procedure.
* gnu/system.scm (essential-services): Use it.
* gnu/system/install.scm (cow-store-service): Mention it in comment.

install: Add GRUB to the set of global packages.

* gnu/system/install.scm (installation-os)[packages]: Add GRUB.

gnu: Add polkit-qt.

* gnu/packages/polkit.scm (polkit-qt): New variable.

gnu: Add guile-sdl.

* gnu/packages/sdl.scm (guile-sdl): New variable.

gnu: Add sdl-union.

* gnu/packages/sdl.scm (sdl-union): New variable.

gnu: Re-synchronize a couple of synopses with the Womb.

* gnu/packages/lisp.scm (gcl): Synchronize synopsis.
* gnu/packages/scheme.scm (mit-scheme): Ditto.

gnu: Add polkit.

* gnu/packages/polkit.scm (polkit): New variable.
* gnu/packages/patches/polkit-drop-test.patch: New file.
* gnu-system.am (dist_patch_DATA): Register patch file.

gnu: Add nspr.

* gnu/packages/polkit.scm (nspr): New variable.

gnu: Add Image::ExitTool.

* gnu/packages/photo.scm (perl-image-exiftool): New variable.

system: grub: Adjust default theme color.

* gnu/system/grub.scm (%default-theme)[color-highlight]: Change
  foreground to cyan, as suggested by Felipe López.

gnu: ffmpeg-2.2: Update to 2.2.10.

* gnu/packages/video.scm (ffmpeg-2.2): Update to version 2.2.10.

gnu: ffmpeg: Update to 2.4.3.

* gnu/packages/video.scm (ffmpeg): Update to version 2.4.3.

services: udev: Make /dev/kvm 666 as a workaround.

* gnu/services/base.scm (kvm-udev-rule): Change /dev/kvm mode to 666 to
  work around <http://bugs.gnu.org/18994>.

system: grub: Add preliminary support for themes.

* gnu/system/grub.scm (<grub-image>, <grub-theme>): New record types.
  (%artwork-repository, %background-image): New variables.
  (<grub-configuration>)[theme]: New field.
  (svg->png, resize-image, grub-background-image, eye-candy): New
  procedures.
  (grub-configuration-file): Use 'eye-candy' and add it in BUILDER.

vm: The 'run-vm' scripts now passes its arguments to QEMU.

* gnu/system/vm.scm (system-qemu-image/shared-store-script): Add "$@" at
  the end of the script.
  (common-qemu-options): Remove trailing newline.
* doc/guix.texi (Invoking guix system): Document it.

gnu: slim: Update URL.

Reported by Felipe López <felipe.lopez@openmailbox.org>.

* gnu/packages/slim.scm (slim)[origin, home-page]: Update URL.