Allow for testing using a peerID

[aschmahmann]

As in noted in #9 (comment), it's not great that users need to figure out which of the variety of addresses their node supports they should be putting into IPFS Check.

If we could let people specify /p2p/YourPeerID and use the DHT to do the lookup that could make this much easier. This will likely require some rewording of the error messages and returned values on the front-end for things to continue to make sense for users though.