Browser version should be able to save Orbit's data files

[haadcode]

Currently Orbit can't save 'orbit-db-cache.json' file in the browser version. This is due to 'fs' not being available in the browser.

Find a library that does this. This should not cause modifications to Orbit's or it's dependencies code.

[haadcode]

Options:
https://www.npmjs.com/package/fs-web
https://github.com/jvilk/BrowserFS

Or we could use what @dignifiedquire suggested:

< dignifiedquire> you could do the same thing we do in js-ipfs-repo
< dignifiedquire> haad: https://github.com/ipfs/js-ipfs-repo/tree/rxjs/src fs-store and idb-store have the exact same api
< dignifiedquire> also https://github.com/maxogden/abstract-blob-store