ImgPlus: add axis copying constructor
ImgPlus: add axis copying constructor

Copying all information from an ImgPlusMetadata may not be
appropriate. However, since ImgPlus does not have a getAxes method,
using a copying constructor is the best option when we do want to
preseve axes.

A ImgPlus(Img, ImgPlusMetadata, boolean) provides control over whether
metadata beyond axis information is copied or not.

imagej/imagej-common