This commit removes few workarounds and explicit setting of CMake policies.

Note that the setting of CMP0017 to OLD (introduced in r16366 (COMP: Update
CMake policy requirements) is not needed. Slicer does not provide CMake
modules that should be included by modules distributed by CMake.

This will ensure the CMake version has:

* support for VS 2015 (introduced in CMake 3.1)

* a decent support for detecting compiler features (useful with C++11 and above)
  See https://cmake.org/cmake/help/v3.5/manual/cmake-compile-features.7.html

* as well as support for modern cmake that will be used to modernize the
  Slicer build system.
  See https://cmake.org/cmake/help/v3.5/manual/cmake-buildsystem.7.html#build-specification-and-usage-requirements

CMake 3.5 is also old enough (release in April 2016) and available (same version
or above) in distributions like these ones:

* Arch Linux
* Ubuntu LTS 14.04, 16.04
* OpenSUSE Leap 42.2, 42.3
* Debian 9, Sid
* Fedora 24/25/26
* Slackware 14.2

See https://pkgs.org/download/cmake

// ------------
Update MultiVolumeExplorer:

$ git shortlog 7e44252..c4d3b65 --no-merges
Andrey Fedorov (1):
      ENH: helper script to get stats for a mv frame

Jean-Christophe Fillion-Robin (1):
      COMP: Update CMake version to 3.5.0

// ------------
Update MultiVolumeImporter:

git shortlog 3fb2858..b2453a8 --no-merges
Jean-Christophe Fillion-Robin (1):
      COMP: Update CMake version to 3.5.0

git-svn-id: http://svn.slicer.org/Slicer4/trunk@26201 3bd1e089-480b-0410-8dfb-8563597acbee