endpoint consolidation

[jmensch1]

Fixes #605 and #511

This changes some of our endpoints to limit database calls and make the api cleaner. The PR looks like a lot of changes, but it's mostly just reorganizing code that was already there.

Visualizations endpoints

We've been hitting three separate visualizations endpoints every time the user clicks "Submit": /requestfrequency, /requestcounts, and /timetoclose. This consolidates them into a single /visualizations endpoint that makes a single request to the database (instead of 3 separate DB calls that ask for a lot of the same data).

Comparison endpoints

We still have three comparison endpoints, since the frontend calls them individually. But this puts them in a single ComparisonService, with new signatures for the endpoints:

/comparison/frequency
/comparison/timetoclose
/comparison/counts

There's a small amount of frontend code here to integrate the new endpoints. I also removed the /pins endpoint and service since we're not using it any more.

• Up to date with dev branch
• Branch name follows guidelines
• All PR Status checks are successful
• Peer reviewed and approved

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[adamkendis]

Front-end changes look good. I looked through the back-end changes but not in great detail.