Create a web version with `react-native-web`

To get to the vision in the "Why?" section -- build for all 3 codebases simultaneously. This does limit the usage of some libraries/components however, as they have to be built to be used on all 3 (typically they're only for mobile or for web).

The web version could also be used/demo'd immediately, no need to download/install an app.

Ejecting Expo and figuring out some custom Haul/spinjs/webpack integration in addition would make it most of the way there.