Don't run repository intialization handlers too early

Repository intialization handlers (subclasses of RepositoryInitializationHandler, and especially RouteModelsInitializator) run too early: they may do work that need to be logged to the Audit through a sync post-commit event that doesn't wait for all bundles to be started, including the Audit itself.

The main symptom is this log during startup:

ERROR [Nuxeo-Event-PostCommit-1] [NXAuditEventsService]
Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined

Let's run the initialization handlers in afterStart to avoid this.