bank_account_statement display proper currency amount in tooltip

When processing a bank statement reconciliation for a journal in a different currency than your home currency a user does not necessarily know the exchange rate for the foreign currencies he is processing. My PR will assist user with this information.

***Impacted versions:***

 - 8.0

***Steps to reproduce:***

 1. Create a bank statement for a journal in a different currency
 2. Add a line where where amount is zero and type anything in the amount_currency
![screen shot 2014-08-08 at 11 35 24 pm](https://cloud.githubusercontent.com/assets/7885477/3864951/498d6416-1f77-11e4-9991-b3dcf6dcec23.png)

 ***Current behavior:***
![screen shot 2014-08-08 at 11 21 15 pm](https://cloud.githubusercontent.com/assets/7885477/3864956/70115304-1f77-11e4-885c-1d673be82690.png)

***Expected behavior:***

![screen shot 2014-08-08 at 11 26 19 pm](https://cloud.githubusercontent.com/assets/7885477/3864959/8037f878-1f77-11e4-9999-8e8eef01fd4f.png)