Refactor out the code creating an ImageStack from a Dataset

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
GrayImagePlusCreator: force XYCZT for cell images

Before letting ImgLib-ij wrap a CellImg as a virtual stack, we *need* to
make sure that the axes have the expected order: ImageJ 1.x' VirtualStack
assumes implicitly that the dimension order is XYCZT.

This assumption is broken e.g. when loading at least some OME TIFFs:
See https://github.com/imagej/imagej-plugins-commands/issues/6

[jes: split up commits, used MixedTransform directly instead of having
nested MixedTransforms, fixed min/max of added axes (in contrast to
pretty much every other library, ImgLib2 has *inclusive* max valuesi),
prettied up the commit message]

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Let Eclipse clean up GrayImagePlusCreator's source code

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>