Calculate price for orders, trades, and average traded price

[anxolin]

Make it easier for consumers to check the price by doing the calculation already. For that, we need to take into account the decimals of the tokens.

Includes

• [ ] Limit price for an order
• [ ] Average traded price for the order. As the weighted avg price of all the orders ---> sum(soldTokens) / sum(soldTokens)
• [ ] Trade price