Update ImgLib2 dependency to 2.0.0-beta-18

Among other things, this adds a new ImgPlus constructor that we need in
order to create ImgPlus objects with CalibratedAxis objects. It also
fixes the ImgPlus#copy() method to completely preserve CalibratedAxis
metadata by using CalibratedAxis#copy().
RestructureUtils: improve createImgPlus method

This removes uses of the deprecated calibration approach in favor of
cloning the input CalibratedAxis objects properly.

This change also introduces a proper generically typed method for
creating a new ImgPlus from an input ImgPlus template. It retains the
Dataset signature but leans on the new method to do its work.