First phase of support for cross-artifact boundary relationships in
derived content.  The WSDL deriver will now find references by 
searching the repo as well as by looking within the owning document.
Next piece of this is to support resolution of artifacts within the
same s-ramp archive (batch).
Added a new persistBatch() method to the persistence manager to be used
by consumers wanting to add a batch of artifacts at the same time (e.g.
when uploading an s-ramp archive).

Also implemented cross-artifact relationships in the WSDL deriver.  Now
the deriver will set up relationships from derived content to other
derived artifacts from other source artifacts.  In other words,
relationships will be set up even if the target was already in the
repository rather than being part of the source.
Merge pull request #252 from EricWittmann/sramp-113-wsdl-references

(sramp-113) WSDL references across artifacts