Depends on D20266. Boards currently have several `whateverMap<cardPHID => stuff>` properties, but we can just move these all down into a `CardTemplate`, similar to the recently introduced `HeaderTemplate`.
The `CardTemplate` holds all the global information for a card, and then `Card` is specifics for a particular copy in a column. Today, each `CardTemplate` has one `Card`, but a `CardTemplate` may have more than one card in the future (when we add subproject columns).