Refactor to use Libp2p directly

[tabcat]

Have been avoiding using the libp2p provided by ipfs because it is not available when using ipfs via the ipfs-http-client. Recently have cared less about this use-case.

The two pieces to be refactored to use libp2p directly are:

• Opal class makes ipfs.libp2p directly available #29
• Replace Keychain with libp2p keychain api #32
• Peer Monitor uses Libp2p api #31

The peer monitor will benefit from being able to listen for updates instead of polling.

Replacing the Keychain with libp2p.keychain will nullify headaches around the KeyChain not being exported in the first place.

In the further future, will be able to use libp2p protocol handlers to build the BEC push replicator.