COMP: Bump CTK version.

Sync with Slicer.  Fixes CMake configuration warnings.

CMake Warning:

  Manually-specified variables were not used by the project:

    ExternalProjectsContrib_DIR
    PluginsContrib_DIR

Change-Id: I84b35ff4b5c34f33822d71c7d0c79817616e9fb9
STYLE: Space before parens in External_ImageViewer.cmake.

Change-Id: I8c8835bc6a4a3891fd7387031f021ed477300fe3
Merge topic 'CTKBump'

cd223b3 COMP: Bump CTK version.
Merge topic 'ExternalStyle'

950b2a4 STYLE: Space before parens in External_ImageViewer.cmake.
ENH: Cleanup ObjectDocuments classes and add basic tests

Change-Id: Ia5a27b73f37d9f52e215ef784bb21373029034d5