ENH: adding a global Kernel Enum type for morphology

This patch adds a CreateEnum method internal for filters, and the
KernelEnum type. The enum names utilize the sitk prefix as is
convention.

The old class base enums are still this but, there may be some
compatibility issues.

Change-Id: Ia324b5805873ad69e05e817bd2cdc2a82678fd7b
Updating JSON morphology for global KernelEnum

Change-Id: Idc5297e8e8ab2b3e6af9dad09ce2971c0b3887e3
Merge topic 'SIMPLEITK-431_AddMorphologyKernelEnum' into next

c648b62 Updating JSON morphology for global KernelEnum
1fa3606 ENH: adding a global Kernel Enum type for morphology