Make sure to keep wcs attribute of enmap

[xgarrido]

We should preserve wcs when manipulating so_map object. This line

pspy/pspy/so_map.py

Line 782 in cca8cf1

noise.data = np.random.randn(size[0], size[1]) * rms_uKarcmin_T / np.sqrt(pixArea)

removes wcs information : we must use noise.data[:] to only modify the numpy array and keep wcs unchanged

[xzackli]

This can be solved with np.copyto, if my understanding of the ndarray interface is correct?