Add option to buy/sell securities in a separate currency to the unit price

[IsaacCheng9]

Summary

• Currently, we only have the option for users to record transactions bought/sold in the same currency as the security's unit price.
  • If they bought it with GBP but they provided a unit price in USD, they have to manually convert GBP into USD for the amount paid, or convert the unit price to GBP.
  • For example, if I bought £500 of AAPL, I would have to manually convert this paid amount into USD to input the transaction accurately.
• We should have two boxes, where the user either enters the amount bought in the given currency, or the amount bought in GBP.