Refactor the original metric tracking class for merge request information

We created the original HLL class for tracking unique users here

Since then, we have a better understanding of the requirements of the metrics we need, how to split them and the analytics team has created code we can use. We should stop tracking everything together, and track things individually, and then join them up after wards.

The problem is that we would have to do this in multiple steps as we already have periscope data based on these usage data metric keys.

1. Create new keys for each action in this file
2. Save both, the current joint keys, and the new individual keys to HLL
3. Wait a month so the data in the individual keys catches up to the joint keys
4. ???
5. Switch over the usage data to use the the PFCOUNT'd data for the same usage data key
6. Remove the track_unique_events class and/or simplify the methods