JCLOUDS-457: BlobStore MultiPartUpload strategy

The code related to the MultiPartUpload strategy has been added.
MultiPart uploads use an upload strategy (e.g. sequential vs parallel)
and also a slicing strategy to split the payload in different parts.
This slices a 100 MB download into (12) 8 MB parts and (1) 4 MB part.  Does the square root heuristic create too many parts for smaller blobs?