DS-2348 REST Bitstreams should be only in original bundle.

http://jira.duraspace.org/browse/DS-2348

Better logic at adding bitstream to bundle. It checks if bundle original exists. Than add bitstream to it or create bundle and add bitstream to it.
This whole routine is the same as `Bundle[] bundles = dspaceItem.getBundles("ORIGINAL")`, I would use that instead.