Use the Config mode of find_package to search for ITKConfig. This makes
FindITK a thin-wrapper around a standard find_package, bringing benefits
like searching lib64 paths when appropriate. This does for FindITK what
commit 2c1a01dc (Modernize FindVTK module, 2009-10-07) did for FindVTK.
This adds copyright/license notification blocks CMake's find-modules.
Many of the modules had no notices at all. Some had notices referring
to the BSD license already. This commit normalizes existing notices and
adds missing notices.
