Add operator overloading for sitk::Image in C# wrappers.

For the moment the equality operators (== and !=) are not
overloaded due to issues. See:
http://msdn.microsoft.com/en-au/library/ms173147(v=vs.80).aspx

Change-Id: Ief4796f2e575bb02101a238ef7437b0817053e24
Checking images in CSharp image operator tests

Change-Id: I5ed02131b6210e8595631b682446277c9828775a
Merge topic 'SIMPLEITK-389_CSharpImageOperatorOverloading'

ca8486e Checking images in CSharp image operator tests
a1ac201 Add operator overloading for sitk::Image in C# wrappers.