As a user, I want to apply my own drink-to-food price ratio

[knoffi]

• [ ] base price should a price ratio for drinks:food (default 1:2, or 150%)
• [ ] user can enter a rational number or percentage (from 0 to infinity) to regulate price ratio
• [ ] short explanation text for price ratio
• [ ] adjust price display to price ratio
• [ ] adjust shopping card and buying process to price ratio