move IdentifiableDaoBase.findByReferenceTitle() into ReferenceDao
findByReferenceTitle() searches for "title" which only exists in
Reference.class therefor it makes no sense having this method in service and dao classes for IdentifiableEntities. This is confusing as the method name can be interpreted in various ways depending on the base class. e.g. Think on TaxonService.findByReferenceTitle() this refers semantically to the nomenclatural reference.