Add ->instanceOfStorage to handle instanceof for storage wrappers

Conflicts:
	lib/private/files/storage/common.php
	lib/private/files/storage/wrapper/wrapper.php
	lib/public/files/storage.php
Use instanceOfStorage instead of instanceof

Conflicts:
	lib/private/files.php
Fix storage wrapper being called with null
Pass any methods custom to specific storage implementations to the wrapped storage
remove duplicate declaration of isLocal()