Patch release: Introducing list meta

This release is a major step toward long-term stability, with the introduction of list-meta documents. The list-meta docs are responsible for story order, and allow us to move a story with one write to the database, allowing us to migrate away from our ad-hoc transaction system, which has been the source of instability issues for a few years.

This release is compatible with all existing Circle Blvd clients, as the client API has not changed.

This release also fixes the checklist functionality, which was broken in the 1.5.10 release.