PERF: ImageAlgorithm::copy to use std::copy for conversion

The prior implementation used memcpy, with the restriction that the
internal pixel types be the same an POD. With the nice change to use
std::copy, this restriction is not required, just that the pixel
types are convertible, and that the dimensions are the same.

I have observed over a 10X improvement for 3D images between std::copy
method vs the iterator based one. Also this enables the CastImageFilter
to use std::copy, yielding to 25X speedup the performance compared to
v4.3.2.

Change-Id: Ifdb80c1c5d726fdc301205d0d6a8111ea1782e83
Merge topic 'ImageCopyUse_stdcopy_ForConversion'

68372d2 PERF: ImageAlgorithm::copy to use std::copy for conversion