Feature: IMDB support

For public figures, IMDB represents an interesting way to extend validation.

For instance, http://imdb.me/LeifSawyer is the short-url to my IMDB entry.

I'm not yet sure how to tie the two accounts together, but perhaps with the IMDB-pro accounts it would be possible.

No file, test, or entry point is named. Start by examining how Keybase currently validates or links public-figure identities, then determine whether IMDB or IMDB Pro can provide a verifiable account relationship. Done would require an agreed integration design and implementation scope.

Written by the indexing model from the issue text.