Including amount of time spent actively quantifying in exported csvs

[mattyg]

It would be great to have metrics on the amount of time it takes for a quantifier to complete their quantification assignments. They could be included in the exported csv and used in RAD dashboard analysis. It would also be a valuable metric for improving #178

Implementation Options

• We could potentially use the data from praise.quantifications[x].updatedAt, and an algorithm to estimate an "activity time" from all those updates times. For example this algorithm: https://github.com/kimmobrunfeldt/git-hours#how-it-works
• Alternatively, we could implement a mouse-tracking timer. If a user is on the QuantifyPraiseReceiverPage, and their mouse is moving, a timer starts locally. When their mouse stops moving for longer than a certain threshold (say 30 seconds), then the time is sent to the api and added to their "active quantification time" for that period.