Update ITK superbuild to the official 4.7.0 release

Change-Id: I1689f04ce55802713b4b4ea0f3565f7f1d87136f
Merge branch 'SIMPLEITK-585_UpdateToITK4.7' into release

* SIMPLEITK-585_UpdateToITK4.7:
  Update ITK superbuild to the official 4.7.0 release

Change-Id: I34e3d334ca231f457dfe6e0bb8f57f15df03cf2c