Add WNFS support

[icidasset]

https://github.com/wnfs-wg/

[icidasset]

User storage layer almost done on the fission branch.
Music storage layer is more difficult.

Diffuse needs:

• Service worker proxy so we can make HTTP range requests.
• Ask user for access to their Music directory

Webnative (fission) needs:

• Streaming decryption for private files (needs to have offset and length, just like with ipfs.cat, to work together with HTTP Range header)