Create a separate start-up currency list

The user will have to go through three setup stages for the app.

 - implement a separate StartUpCurrencyListActivity where the user will
   choose their initial currency
 - Connect StartUpCurrencyListActivity with StartUpBudgetLengthActivity
   when the user chooses the currency.
 - The user is now able to go back to StartUpCurrencyListActivity to
   change their choice of initial currency.