ENH: Converted Multidimensional splitter to new base class

Ported the old ImageRegionMultidimensional splitter to new
template-less base class.

BUG: When then starting index of the input region was non-zero, the
splitting was erroneous. This is now fixed.

Change-Id: Ib0de93267bebdbd8a3edbae7e142b1a21b330ed6
Merge topic 'ConsolidateImageRegionSplitting_Multidim'

c5cbbb5 ENH: Converted Multidimensional splitter to new base class