Use the File System Access API

[NickGeek]

Is your feature request related to a problem? Please describe.
See #309 and others.

Describe the solution you'd like
Use this API to save files locally on the FS instead of via IndexedDB. Potentially this could be a more manual thing,
just enabling Ctrl+S to happen without a prompt or something because the format of the files in the IndexedDB are a little janky.

Additional context
This will either need to only partially go out or wait until FF and Safari support the feature: https://caniuse.com/native-filesystem-api