Card: Simplify API

[charlieTheBotDev]

Context

The current card API (e.g. hx.card.x.x.x) is complex and leads to a lot of complexity for both the user and the code.

The API should be simplified to allow something like:

card()
  .add(cardGroup()
    .add(cardSection())
    .add(cardSection({ fixed: true }))
    .add(cardSection({ joint: true })))
  .add(cardGroup({ vertical: true }))