Add support for saving non-planar images

[ctrueden]

Currently the ImgSaver only supports planar type ImgPlus objects. This support should be generalized to support any type of ImgPlus.

Migrated-From: http://trac.imagej.net/ticket/1083

[dscho]

I fear that we'll have to step up efforts to implement this. Maybe a little less if the heuristic to load CellImgs is made less overzealous, but still: when users load virtual stacks via ImageJ2's SCIFIO support, they'll want to be able to save them with proper metadata (as opposed to the limited TIFF support of ImageJ 1.x). We should make that possible and easy.

[hinerm]

See https://github.com/scifio/scifio/tree/write-nonplanar-types for work on this issue