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.
fritzing: add version 0.9.0b

- An open source prototyping tool for Arduino-based projects
megaglest: new package
pythonPackages.cvxopt: added package
screen: enable 256 colors
Improve name quoting to correctly handle underscore
Update vanity counter. Now with GitHub username support
lua-packages.nix: whitespace fixes
Merge pull request #4502 from grwlf/screen-256color

screen: enable 256 colors
haskellPackages.cmdtheline: apply System.{Cmd -> Process} patch
Merge pull request #4501 from edwtjo/cmdtheline-patch

haskellPackages.cmdtheline: apply System.{Cmd -> Process} patch
Merge pull request #4475 from matejc/megaglest

megaglest: new package
Merge pull request #4456 from robberer/pkgs/fritzing

fritzing: add version 0.9.0b
Merge pull request #4392 from cstrahan/logstash

logstash service improvements