Eliminate deprecated IntervalUtils usages
Add placeholder classes for ImgPlus

While the ImgPlus class is fundamentally broken, we need a stopgap to
completely migrate away from the net.imglib2.meta package. We cannot
just use net.imglib2.meta.ImgPlus mix-and-matched with net.imagej.axis,
net.imagej.space and net.imagej.interval because the type hierarchies
would be inconsistent (e.g.: net.imglib2.meta.ImgPlus does not extend
net.imagej.interval.AbstractCalibratedRealInterval).

So we introduce the temporary classes ImgPlus, ImgPlusMetadata,
ImageMetadata and Sourced into the net.imagej package, which extend
the appropriate non-deprecated classes.

After the addition of these classes, it will be possible to migrate
the net.imagej.* classes fully away from net.imglib2.meta.
Eliminate deprecated net.imglib2.meta usages

There is still much work to be done cleaning up the ImgPlus class and
related interfaces. However, this is an important first step.