DOC: Update GDCM license information.

Change-Id: I13698f63ec51091669e36781c2819e06a070c829
DOC: Update footnote about ITK license.

BSD -> Apache.

Change-Id: I89cd441d131c3a1cec63c09cc39976a9ab5e17aa
Merge changes I89cd441d,I13698f63

* changes:
  DOC: Update footnote about ITK license.
  DOC: Update GDCM license information.