Added naive RandomAccessibleROI implemenation

	* this will be replaced with more sophisticated imglib2 ROIs
	* as soon as they are available in ImgLib2
	* this is just a placeholder
Merge branch 'descriptors' of https://github.com/scijava/scijava-ops into descriptors

Conflicts:
	descriptors/src/test/java/org/scijava/ops/descriptors/SimpleTesting.java