Add browser extension support

[bgins]

Summary

Problem

Webnative does not expose information in a way that is accessible to browser extensions.

Impact

Browser extensions cannot easily interface with apps that use Webnative.

Solution

Implement an API that browser extensions can interface with to query Webnative for:

• Webnative version
• App namespace
• Username
• Account DID
• Agent DID
• Filesystem skeleton
• Data root CID
• Capabilities (what parts of WNFS does the app have access to?)
• Bitswap activity and connection details (Maybe not? We may be abandoning bitswap soon.)

The information should only be exposed when the developer has set debug to true when initializing a Webnative program.

Webnative should send messages to a browser extension when any of the above values change. We want to avoid polling for changes.

[bgins]

A couple of early thoughts about implementation.

We could add a webnative property to a global like window.navigator to expose the information. This would make the information available, but we would still need to send messages when values change.

We may also be able to implement this entirely with message passing. Rather than exposing the values on a global, send a message at initialization and with each update.

[jeffgca]

Some initial bootstrapped code is here:

https://github.com/therealjeffg/webnative-devtools

[bgins]

Tracking issue for work on the extension: https://github.com/webnative-examples/webnative-devtools/issues/2

[bgins]

Issue covering communication with the extension: https://github.com/webnative-examples/webnative-devtools/issues/8