Redis key is now incremental

[fjoniyz]

Problem: Until now the way that the entries were added to the Redis persistence, was using random keys. This led to a change of order of messages inside the cache as the keys are in an ascending order.

Solution: get all keys, cast them to ints, order them and then get the value for each of them by casting them back to strings

[nomorehumor]

This has to be updated to conform to newest type of our data in redis (hashes). Apart from that it looks good, after updating we can merge it.