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.
logstash service improvements

* add logstash-contrib plugins package
* add additional options to the logstash service
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.
keepass: Bump version to 2.28
fritzing: add version 0.9.0b

- An open source prototyping tool for Arduino-based projects
golang: add golint and gotags
libsieve: new package
discount: new package
stunnel 5.05
icedtea7 requires giflib 5.0
mpd: fix URL

Stable is now 0.19; we're not updating to 0.19 yet because upstream
forgot to include a necessary file in the 0.19 tarball.

FTR 0.19 requires boost and icu as dependencies

cc @astsmtl
sxiv: 1.1.1 - 1.2
sxiv: add missing patch
ised: get rid of builderDefsPackage
Update xmobar to 0.22
xmobar needs mtl 2.2.1 and transformers 0.4