Adding overloaded output operator for PixelIDValueEnum

Change-Id: I63bfe0d884a82a03c4775196cabf310c2cf20e27
Enable printing of pixel enum in filters.

Change-Id: Ib0fa64f9c1e1b5e7b3239c1034b7feef87d68270
Merge topic 'SIMPLEITK-469_AddPixelIDValueEnumOutputOperator' into next

51afd003 Enable printing of pixel enum in filters.
0e687382 Adding overloaded output operator for PixelIDValueEnum