Add manual price for cards with no price data

Some cards (especially rare/foreign cards) have zero price data available. This can throw some deck prices (example: https://moxfield.com/decks/ut7r1PSZVUKMmaslK7_KOw) off by huge percentages.

Having the ability to manually set a price would be fantastic. Then, instead of showing no price for the card, it would use the set price - however if in the future a price was made available through normal methods, the manual price would then be over written.