Add UserSession::resource_states specs
Add basic collect_states methods and redirect them to persistor class.
Update specs for UserSession.revisions
Clean  SessionFinder::Persistor unused methods.
Add UserSession::revisions and specs.
Find direct revisions from session works.
Fix method in wrong block.
Implement RevisionFinder using Persistor dependencies.
Add ReadOnly Sessions and Persistors.
Add UseRevisionTables module.
Add Revision::Session#object_states
Fix indentation
Add UserSession#revisions_for
Add Revision#state attribute (instead of #resource).
Lookup persistor from table_name.
Select distinct id in ids_for
Add dependency concept and register them.
Fix UserSessionPersistor#collect_related_states.

And add :depend attributes to parent relation.
Remove breakpoints.
Clean Persistors