Feature/house of cards intro

[Blizzardsev]

Introduces the following:

• New intro event event_house_of_cards, where Natsuki's antics with the card pack go about as well as planned
• Two new desk items for use in future events/idles:
  • jn_house_of_cards
  • jn_card_pile

[Blizzardsev]

Preliminary pull request while awaiting art assets delivery for the new desk items: can still be reviewed on the basis of dialogue.

This should not be merged in until those assets (or alternatives) are in place.