[Eventonica] Update React portion

[vegetabill]

A child of the Eventonica epic: #1296

Modify Old Eventonica Part 7 to match new reqs in README

This should build a browser app with no API. All data should be in-memory using the code from Part 1.

A prereq for doing this part of the project is a still-unwritten React Part 4 lesson #1337

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[vegetabill]

We decided not to change the order of React and Eventonica so this issue is no longer needed