Improve Keybase Integration

[w4]

We're currently using Keybase to get all the users that have "proof" of ownership of the domain we're loading a script from, ask the user whether they'd like to trust them and then grab all the 'trusted' public keys and use them to verify the scripts are signed.

Right now we just show the user the Keybase user's username when asking whether or not they want to trust the user. We should make use of Keybase's vast amount of "proof" that a Keybase user is in fact a person that we trust by showing the end user some of their details.

We should also pin 'trusted' users by more than just their username as we don't take into account identity proofs being revoked, potentially indicating that the Keybase account is no longer under the trusted person's control.

[w4]

As of c28127d the browser action has a KeybaseUser object for each user, we can use this to make a nice profile page