Add storage and cache wrappers to jail a storage to a subfolder

lib/private/files/cache/cache.php

lib/private/files/cache/wrapper/cachejail.php

lib/private/files/cache/wrapper/cachewrapper.php

lib/private/files/storage/wrapper/jail.php

lib/private/files/storage/wrapper/permissionsmask.php

tests/lib/files/cache/cache.php

tests/lib/files/cache/wrapper/cachejail.php

tests/lib/files/storage/wrapper/jail.php