[v6r13] Clean-up and changes in the Storage classes

These are a number of changes in order to simplify the logic of the Storage classes:

    single place where the PFNs are constructed from LFNs ( StorageBase.getPfn() )
    multiple methods from specific Storage classes are moved to StorageBase
    StorageFactory creates Storage objects using a standard plugin mechanism ( ObjectLoader )
    allow to define VO specific path in the SE configuration
    check if StorageElement is allowed for the user's VO
    dirac-dms-show-se-status shows only SEs eligible for the user's VO
    fixes in the TestXXX classes
    suppressed ReplicaManager, MetadataCatalogClient
    some bug fixes and minor improvements Those changes are still to be thoroughly tested.