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.
Hmm, I see a potential NPE NullPointerException. bundles.length can't be checked in the case that bundle == null, so I'm thinking that the null/empty check needs to occur before bundles.length.