Add "strike" button to report menu

[sneakers-the-rat]

Pitch

Currently, for a reported post, one can only delete the post, mark it sensitive (if it has media attachments), limit, or suspend the account. Add a "strike" or "warn" button that just adds a strike without taking other actions.

Motivation

We want a way to be able to issue a strike against the account without deleting a post to be able to track patterns of borderline behavior that doesn't quite reach the level of deletion/etc.