keybase.io/verify with prefilled message to verify (or decrypt)

I'd like to be able to create a link like the following:

```
https://keybase.io/verify#message=-----BEGIN%20PGP%20SIGNED%20MESSAGE-----%0AHash:%20SHA1%0A%0AMessage%0A-----BEGIN%20PGP%20SIGNATURE-----%0AVersion:%20GnuPG%20v1%0A%0AiQEcBAEBAgAGBQJVcBZGAAoJEGV/Rg0giUZmIcEH/i5pM0dsXlilp3nHZl/9qquq%0AopmvG8WfduHNfY00EoIYYocxnOSpzj82Y43WRJFnO2BQxD/qAmxJgMzDfWB6zLDh%0AzlTjc1JgpSEVDNSCaMCuBCIQcXV2azG76Iuhx6sHf6CsVUrb3EIvBBZUE4FYbYYv%0AkI1G+cAnDub+x0kAvDABubn1+3FVnzU2s6cXexz/9JxI58Tp4d0P5Vf77EDoYJsp%0AxUFR8YALL6w5zMDG7bv5Q7Tu9+a1y1yn1Itwlvd1DowdJ2GQDH6L7PBf5QJgz84C%0AO5g/wUklDVxU87O6wyhrMx+R0wKzPQeayRcfvMmnBIOOxvEiW8WWkWhHP8BAdT8=%0A=3UOo%0A-----END%20PGP%20SIGNATURE-----%0A
```

(the above is a clearsigned message)

Where someone would be able to click the link, click "Verify", and get a green checkmark (if all is well).

(Or prefill for /decrypt where they can click Decrypt, enter their passphrase, and read the message if the gpg key is stored.)

---

The use-case is supporting GPG messages in [Discourse](https://github.com/discourse/discourse) (another ruby+JS app) by placing them in a specially styled box, showing the plain text and a "Verify" button (or a box saying "This message is encrypted. [Decrypt on keybase.io] [Decrypt with other program]").

That neatly sidesteps the key-storage problem for us. (The key-discovery problem is harder - there is an unbounded number of Discourse instances, your username could be different on every one. That is an issue for another time, though.)

Start at the keybase.io/verify entry point and review how the URL fragment is handled, along with the existing Verify and Decrypt flows. Done means a link can prefill a clearsigned message for verification and support the proposed encrypted-message handoff, including the success or passphrase behavior described.

Written by the indexing model from the issue text.