f8d5e310a7
Added interfaces for common abstractions needed to implement historiography. A Revision is an entity associated with some RevisionMetadata. That in turn consists of a revision number and date at least and is backed by a implementation specific delegate. The Revisions wrapper class allows accessing the latest revision from a list of Revision instances no matter what order they are in. A RevisionRepository allows access the revision an entity was changed in the last time, access all Revisions of an entity as well as paged access to it.