COMP: Add Tiff and JPeg build to support DCMTK

[Chaircrusher]

There are several important parts to this patch, and it involves using custom github versions of both ITK and DCMTK. Eventually this will no longer be necessary, once the changes in our private versions are pushed into the official versions of those libraries.

1. DCMTK is modified to generate proper CMake config files in both the build tree and the installed tree.
2. ITK is modified to use find_package(DCMTK NO_MODULE), in the case (as with BRAINS) where ITK_USE_SYSTEM_DCMTK is true.
3. Add local JPEG & TIFF builds.

The reason for all of this is that DCMTK was not exporting its dependencies (e.g. ZLIB, JPEG, TIFF) properly, so when BRAINSStandAlone got built against ITK (which was using BRAINStandAlone's build of DCMTK), the library list exported by ITK didn't include DCMTK's dependencies. The new DCMTKConfig.cmake does the exports properly, so that linking against ITK works properly.