JCR-3718 Inconsistent Principal Validation between API and Import behavior

- make principal check based on ACLProvider configuration
- adding new ACLProvider configuration parameter: "allow-unknown-principals", default: "false"
- make missing-principal bypass in AccessControlImporter based on configuration
- adding new AccessControlImporter configuration parameter: "importBehavior", default: "bestEffort"


git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/trunk@1560783 13f79535-47bb-0310-9956-ffa450edef68