INT-3177: Generic RedisInboundChannelAdapter

Port from Spring XD: allow for `RedisInboundChannelAdapter`
to receive from Redis any object, not only String

* Make `serializer` property 'resettable' to `null`
* Change `RedisInboundChannelAdapterParser` to allow to apply
empty value from `serializer` attribute
* Add parser test and test for `byte[]` messages