Created: (JCR-1721) make collection element names configureable

make collection element names configureable
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                 Key: JCR-1721
                 URL: https://issues.apache.org/jira/browse/JCR-1721
             Project: Jackrabbit
          Issue Type: New Feature
          Components: jackrabbit-ocm
            Reporter: Oliver Lietz
            Priority: Minor
         Attachments: jcrElementName.diff

- add jcrElementName to CollectionDescriptor and Collection annotation
- make COLLECTION_ELEMENT_NAME protected instead of private