OMEXMLMetadata: remove unnecessary import
OMEXMLMetadata: remove unnecessary public modifier
Eliminate explicit uses of OMEXMLMetadataImpl

The resolveReferences method belongs in the OMEXMLMetadata interface,
rather than as a public method of its implementation.

Once the interface itself declares the method, the various explicit
casts to OMEXMLMetadataImpl are no longer needed, and interface-driven
design works to keep the codebase extensible.
Merge pull request #479 from rleigh-dundee/ome-xml-service-dev_4_4

Improve OMEXMLMetadata (dev_4_4)