Strips Next.js from this repo

The Next.js boilerplate we started with was slowing development down because it assumed we'd be using Next's api routes — whereas we're using Firebase's cloud functions. (Specifically, this presented a problem when trying to persist Firebase Auth's sessions, and when trying to restrict access to individual pages based on authentication). Since we were statically hosting the output of Next, we weren't even taking advantage of the benefits that come with SSR. And to top it all off, our target audience has limited utility for those SSR benefits, too.
So, we ported the Next.js app into a plain React app. It is located here -> https://github.com/Neighbor-Army/frontend. The commit history is intact; it's just a fork in the road.
Back to this PR, it strips the Next.js stuff out of this repo. There is only Firebase functions related code in here now.
Tests are still passing. And README instructions are updated as well.
Still a big PR, though, so please pull down and double check things before merging.

Neighbor-Army / help-with-covid