As a user, I want to manage stocks/currencies/securities within an account so I can track wealth

Ideas

[ ] New view under Budget: securities. Folks can add security names (dollar, euro, stock, etc) along with interesting data
[ ] Use some kind of finance API for pulling in security data
[ ] Accounts have a new tab, securities(?)
[ ] Within securities, users can track buy/sell orders, as well as set a default currency/stock value for the remaining balance
[ ] Generate values for realized/unrealized gains
[ ] Use default display currency to convert all the values