ENH: Adding output operator for KernelEnum type

Change-Id: I7ed4c0b1468cf9c5e57b4acd16188c5686406a8f
Merge topic 'SIMPLEITK-454_AddEventCallbacks' into SIMPLEITK-468_AddOutputOperatorKernelEnum

Conflicts:
	Code/Common/src/CMakeLists.txt
	Testing/Unit/sitkCommonTests.cxx

Change-Id: If3af07ed8a22d6f4926e1805bbeaa19d856375cc
Merge topic 'SIMPLEITK-468_AddOutputOperatorKernelEnum' into next

2bc36e3d Merge topic 'SIMPLEITK-454_AddEventCallbacks' into SIMPLEITK-468_AddOutputOperatorKernelEnum
74b036d1 ENH: Adding output operator for KernelEnum type