Add Gaia-centric file browser / data explorer / finder

[friedger]

While developing, it would be convenient to have debug/developer page of the browser that shows all files of gaia for localhost (or any app url) with a link to the encrypted and unencrypted content (you never know what you need).

UPDATE: This issue is about data explorer on gaia in general

[moxiegirl]

@friedger couldn't we have a console level command for this?

[markmhendrickson]

@friedger I'm wondering if makes sense to re-title this issue so that it's more expansively about browsing one's data as stored in Gaia across apps in contrast to browsing them for a specific app?

The idea for a Gaia-centric file browser / data explorer / finder seems to come up in conversation often, and I'm not seeing an existing open issue that captures the idea, so I'm thinking your issue here could become the canonical issue for collecting ideas about it.

[friedger]

Implementation can be found here under MOZ 2 license: https://github.com/MichaelFedora/mercurius