BUG: Fix launcher settings to allow loading of extension in unix build tree

This commit restores the correct loading of extension installed in a Slicer
build tree. It contains a fix related to ITKv4 transition and fix related
to transition from DCMTK static libraries to shared libraries (r21914)

Following the transition to ITKv4, the libraries (*.so) were built in the
lib directory [1] whereas in ITKv3, the libraries were built in the bin
directory [2].

[1] https://github.com/Kitware/ITK/blob/1839b74bacfd455dd917b086466c882ed29606ba/CMakeLists.txt#L164-174
[2] https://github.com/Kitware/ITK/blob/v3.20.1/CMakeLists.txt#L93-99

Following the transition to using DCMTK shared libraries (r21914 [3]), a
follow-up commit (r21942 [4]) has been pushed to ensure Slicer could be
started from a build tree on windows.

[3] http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=21914
[4] http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=21942

In both case (ITKv4 and DCMTK), Slicer could be started successfully from
a build tree on Windows (thanks to the launcher settings), and started
successfully on Unix system (thanks to rpath). On the other hand, since
the launcher settings were incorrect on unix system, the loading of
installed extensions (having rpath stripped) in a unix build tree was
failing.

Fixes #3218

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22170 3bd1e089-480b-0410-8dfb-8563597acbee