Replacews/Refactors DescriptionDocumentWrapper with OpenvaultAssetFetcher.
The new class and methods are more descriptive of actual functionality.
Extraneous methods have been removed.
Tests that actually test the AssetClassifier have been removed, focusing
  instead on the nearest interface of the class in question.
All in the name of making the code clearer. So hopefully, that's true :)
* Changes behavior of Openvault::Pbcore::Ingester#ingest when the :replace_if_exists flag is set.
    Before, it would replace the Fedora object no matter what. Now it will only replace if the
    updated pbcore requires that that the object be reclassified as a different model.

* Refactors Openvault::Pbcore::DescriptionDocumentWrapper into a new class,
    Openvault::Pbcore::OpenvaultAssetUpdater. It's a little more semantic in class/method naming,
    and it gets cuts out some cruft.

* Gets rid of the ':ids' option for PbcoreDescDoc factory; use :all_ids instead.

* Gets rid of typo directory 'spec/models/datasream'.
Merge pull request #1020 from afred/refactor-description-document-wrapper

Refactor description document wrapper