Serendipitous question pools

This isn't high priority, but it'd be nice to define multiple ways to ask the same question on serendipitous cards, just to make things feel a little more fluid and less robotic. For example, when we roll `description` for some content, being able to randomly pull from "Describe %{name}.", "How would you describe %{name}?", "How do people usually describe %{name}?" instead of always just asking the same way.

Start by locating the serendipitous card implementation and the code that rolls the `description` prompt. Determine how question text is currently selected, then add support for choosing among multiple equivalent templates for a card. Done means description prompts can vary while still substituting the content name correctly.

Written by the indexing model from the issue text.