Add paging ability in Directory API

It should be usefull in some case to have API to only select a subset of query result in the Directory API.

The problem is to have an efficiant query in all directories implementation.

In a first approach, only org.nuxeo.ecm.directory.sql.SQLSession take advantage of an optimized query using org.nuxeo.ecm.core.storage.sql.jdbc.dialect.Dialect#addPagingClause.
Others have a fallback fetching all results to subset the whole list.