Issue commands to Nuance items, at least roughly

Summary:
Ref T12738. This makes clicking "Throw In Trash" technically do something, sort of.

In Nuance, the default mode of operation for actions is asynchronous -- so you don't have to wait for a response from Twitter or GitHub after you mash the "send default reply tweet" / "close this pull request with a nice response" button and can move directly to the next item instead.

In the future, some operations will attempt to apply synchronously (e.g., local actions like "ignore this item forever"). This fakes our way through that for now.

There's also no connection to the action actually doing anything yet, but I'll probably rig that up next.

Test Plan: {F4975227}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12738

Differential Revision: https://secure.phabricator.com/D18010