Related to issue #1451: Send snapshot created_at instead of at_date to front for display consistency

[Didayolo]

Original PR: #1461

A brief description of the purpose of the changes contained in this PR.

This piece of code fixes the inconsistency of the date send as the 'last snapshot date'. Before, the usage history tab in the analytics page was getting the correct date (created_at date) from the backend, and other tabs were getting the incorrect date (at_date date) from the backend. Now they all get the correct date.

Issues this PR resolves

Should solve Problem 2 of #1451

Checklist

• [x] Code review by me
• [x] Hand tested by me
• [x] I'm proud of my work
• [x] Code review by reviewer
• [x] Hand tested by reviewer
• [x] CircleCi tests are passing
• [x] Ready to merge