Summary:
In addition to a routine libdef update, we also need to work around a
particularly nasty new bug in Flow, which requires `any`-casts that are
even more unsafe than usual. That said, I think that it’s worth that
cost to remain up to date with Flow, so that we can amortize future such
issues.
Test Plan:
Running `yarn travis --full` passes.
wchargin-branch: upgrade-flow-v0.76.0
Reorganize the code so that we have a single package.json file, which is at the root.
All source code now lives under `src`, separated into `src/backend` and `src/explorer`.
Test plan:
- run `yarn start` - it works
- run `yarn test` - it finds the tests (all in src/explorer) and they pass
- run `yarn flow` - it works. (tested with an error, that works too)
- run `yarn prettify` - it finds all the js files and writes to them