[FEATURE] Overview: Balance pie RT-1697 #deliver

On the "Balance" page, display the total value of the user's balances, as measured in XRP or any currency for which the user has a trust line and which has a well-defined value according to the RippleCharts "exchange_rates" API. Also, display a pie chart indicating the share of value each balance comprises.
Please follow the style guide and don't use hex values.