ENH: Add 'pydicom' python module as external project.

"pydicom is a pure python package for working with DICOM files. It
was made for inspecting and modifying DICOM data in an easy "pythonic"
way. The modifications can be written again to a new file. As a pure
python package, it should run anywhere python runs without any other
requirements.

pydicom is not a DICOM server, and is not primarily about viewing
images. It is designed to let you manipulate data elements in DICOM
files with python code.

Limitations -- the main limitation of the current version is that
compressed pixel data (e.g. JPEG) cannot be altered in an intelligent
way as it can for uncompressed pixels. Files can always be read and
saved, but compressed pixel data cannot easily be modified."
See http://code.google.com/p/pydicom/

The module being licensed under MIT license, it is compatible with
the Slicer BSD like license.

Co-authored-by: Andriy Fedorov <fedorov@bwh.harvard.edu>

From: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22815 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: expose the displable manager and other MRML libs in python

The MRMLDisplayableManager code is needed to access the picker
from a python module.  This feature was added to support
DTI/Tractography processing tools being written by Lauren
O'Donnel.

From: Steve Pieper <pieper@isomics.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22816 3bd1e089-480b-0410-8dfb-8563597acbee