Implement manual stream trimming in Replay

[bwsw]

The problem: per-stream historical pruning is not available because RocksDB allows for a single TTL for the whole column family.

The solution: Add a feature to remove records in the background with the RESTful API. The feature allows users to set a default large TTL for all streams and manage stream trimming by launching background jobs with max:

• stream names (list);
• begin time;
• end time;
• records-per-second cap (max RPS).

RPS is used to avoid excessive contention. E.g., RPS set to 1800 allows cleaning for a maximum of 60 seconds every second the job runs for a 30FPS stream. The RPS is set for a job, not a stream.

Multiple jobs can work simultaneously if needed.