Add a pane to view individual balances

Add a pane containing a list of non-zero balances. Each balance is specific to one issuer, as apposed to the balance list that aggregates balances of the same currency.
Add a link below the balance list that opens the "all balances" pane.

Fixes #659.

![screen shot 2014-08-19 at 2 42 16 pm](https://cloud.githubusercontent.com/assets/3108007/3973604/c51a9c32-27e9-11e4-8f10-ef163f7be305.png)