Allow file access using the browser's local file access API

[timbl]

https://developer.mozilla.org/en-US/docs/Web/API/File_System_Access_API

How to make up the file:/ URI .. have a dummy hostname?
make the hostname a UUID for that device ?

[timbl]

See gitter chat in thread on https://gitter.im/solid/app-development?at=62c6e3bf9f73251a2cecef49