ISIS-2033: major refactoring: IsisSession/UniversalObjectManagerWorking towards IsisSession/UniversalObjectManager being thegeneralization of the current Persistence stack.ConverterForObjectAdapter depicts the new API.Task-Url: https://issues.apache.org/jira/browse/ISIS-2033
ISIS-1976: refactors ParentedCollectionOid constructors into factory classalso renames ParentedCollectionOid -> ParentedOid(since there is nothing collection specific with this oid)Task-Url: https://issues.apache.org/jira/browse/ISIS-1976
ISIS-1976: removes OA map, stream for metamodel, excising guavaKey achievements:Metamodel: almost all guava Function and Predicate idioms removedMetamodel: slight API improvements, such that some of the internal meta-data that is kept in JavaCollections is no longer copied into immutable lists for any calling client, instead Java Streams are returned (which treat the underlying collections un-modifiable by design)the ObjectAdapter per-session map/cache is historythe legacy modules have been removed, for convenince and ease of migration the legacy/transition-1-2- module remains and shall provide legacy glue codeshiro was moved to plugins, and its artifact renamed, to be inline with the other plugins