stumpwm: update and refactoring

This commit updates the stumpwm to version 0.9.8. Futhermore, it
refactors the expression quite a lot:

* stumpwm has been moved from lisp modules to window-managers.
* stumpwm has been added to the window managers NixOS knows about, this
  enables the user to add stumpwm as a default window manager in his
  NixOS configuration like with Xmonad or i3.
* the package has been split into stumpwm and stumpwmContrib. This is
  due to the fact that development of stumpwm and its extension modules
  has been split into two repositories. As of today, the release is the
  last one before this split. This split into two packages only reflect
  those upcoming upstream changes already.

It is planned to make the addition of the extension modules voluntarily,
like with Xmonads option "enableContribAndExtras". Furthermore it might
be possible to add an option to compile stumpwm with clisp instead of
sbcl.
stumpwm: removed from lisp-packages.
Added the grassroots DICOM library.
Added the dlib machine learning library.
Fixed the mirror:// download link for GDCM.
Added Christopher Poole to the list of dlib package maintainers.
Adds the CC-BY-SA-3.0 license
tagainijisho: new derivation

Tagaini Jisho is a free, open-source Japanese dictionary and kanji
lookup tool that aims at becoming your Japanese study assistant.

Homepage: http://www.tagaini.net/
haskell-hsb2hs: add version 0.2
gnome-pomodoro: use fetchgit to be more stable
Update gnome pomodoro using fetchFromGitHub
Merge pull request #4497 from DamienCassou/gnome-pomodoro-url-update

gnome-pomodoro: use fetchgit to be more stable
Merge pull request #4407 from christopherpoole/gdcm

Added the grassroots DICOM library.
Merge pull request #4408 from christopherpoole/dlib

Added the dlib machine learning library.
seeks: upgrade and add optional seeks_confDir
seeks: nixos module
vimb: Update from 2.7 to 2.8
Revert "xapian: update from 1.2.8 to 1.3.1"

This reverts commit b76e8417b3ec2dd1809cd4660f60a6f6c49e42bc.

Breaks recoll, since bindings also need to be updated.
qgis: disable parallel building
rust: updated head

This version include the new "const" syntax.