Flow Editor

The existing Flow display, via Mermaid, is misleading. Policies are not predicates in the traditional sense; they're gates that permit a user to enter a specific stage of a flow, and describe what to do next if the policy does not succeed (fall through to the _next_ stage, or fail the flow entirely).

A better description would be linear, with arrows pointing to wherever the policy leads. It would also allow us to present Flows that look like the rest of our product. This would allow admins to better understand the purpose of the policy. If the drag-and-drop of Custom Dashboard works well, enabling drag-and-drop for the Flow Editor ought to likewise be possible.