User deploy tokens

This allows users to specify deploy tokens with a new syntax, `deploy-token:set` and `deploy-token:reset`.

If a user has a deploy token configured then it will now take precedence over the `HUBOT_GITHUB_TOKEN` variable. This will properly attribute the creator attribute in the API(instead of using a bot's account).
I kinda feel like we should warn people here that this token could be used to clone/push/etc to the repo and enforce only having `repo_deployment` and `user` scopes.