[Proposal] Changes hash to lists on redis.

[adbjesus]

I propose to change hashes for lists on redis. By using LPUSH and LPOP we could keep a sorted list which could simplify pagination (for the default ordering at least), and removal of old samples when there are more than the configured max_samples.

Conceptually the structure inside redis will change from a single hash to multiple lists (one for each worker), i.e.:

sidekiq:worker_stats:Worker1
sidekiq:worker_stats:Worker2
sidekiq:worker_stats:Worker3
...

I don't see any drawback with this, and will look into implementing it soon, but feel free to comment on this in the next couple of days. \cc @Onumis