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.
You can calculate the next power of two more succinctly:

```
partSizeInMB = Long.highestOneBit(fsPartSizeInMB - 1) << 1;
```