Merge topic 'SIMPLEITK-389_CSharpImageOperatorOverloading'

ca8486e Checking images in CSharp image operator tests
a1ac201 Add operator overloading for sitk::Image in C# wrappers.
Merge branch 'master' into next

Change-Id: I35f3fe70fa77276d084a734cb1ff8a4d41bb8bf0