Add overall user stats in Explore right sidebar

[misaugstad]

Resolves #1914

Adds some overall stats for the user to the right sidebar on the Explore page: total distance, label count, and accuracy rating. The most important addition is the accuracy number, which has not been prominently displayed up to this point. The accuracy number has a tooltip that links to your User Dashboard where you can see recent labeling mistakes.

Before/After screenshots (if applicable)

Before

After

Things to check before submitting the PR

• I've written a descriptive PR title.
• I've added/updated comments for large or confusing blocks of code.
• I've included before/after screenshots above.
• I've asked for and included translations for any user facing text that was added or modified.
• I've updated any logging. Clicks, keyboard presses, and other user interactions should be logged. If you're not sure how (or if you need to update the logging), ask Mikey. Then make sure the documentation on this wiki page is up to date for the logs you added/updated.