User dashboard: add leaderboard of some sort

[jonfroehlich]

For individual user dashboards, would be good to add in some aspects of the leaderboard to give them a sense of how they're doing (but hopefully not de-motivating them if they just got started or haven't yet contributed a significant amount).

We could show a snippet of the leaderboard around their current position.

Could also show trophies when they earn certain positions (1st - 9th). Here's a 1st place trophy for missions, for example:

[jonfroehlich]

In order to make this happen, I need the current rank (and total number of users used to calculate that rank) for each of the following individual metrics. Ideally, we'd have this info both overall and for the week.

• Num completed missions
• Total distanced audited
• Num of labels
• Num of validations
• Accuracy

Could also do:

• Speed (with a minimum number of labels/100m and accuracy)
• Rank based on individual neighborhoods as well as overall

[jonfroehlich]

@misaugstad I'd like to add this to the mission sidebars as well. Do you have the backend code for this already as part of @rpechuk's work on the leaderboard? If so, I can start to integrate it not just in the user dashboard but on the mission sidebars as well.

[jonfroehlich]

Because it might be useful to use in the future, here is Google's "CrowdSource" game with badge implementation: https://youtu.be/WmzwfFWEodw. The video shows the user experience for their "validation" interface, their badge system, and their leaderboard.