[TASK] Redis cache backend improvements (Revision 6)

This change contains a drop-in replacement for the current Redis cache backend.
The new backend implements TaggableBackendInterface,
IterableBackendInterface and FreezableBackendInterface, which allows usage for
various caches (like Flow_Session_*, Flow_Reflection_*, Flow_Mvc_*,
Flow_Security_*).

Change-Id: I6eb369c2a9b18ff44206360ef7c948fa9f98e54b
Releases: master
Revision-Id: ef880717800760145ee0e25c049a9eb6d8908b78