Show balances

If the account has balances in other currencies they are aggregated and displayed on the dashboard.
Currently the STR balance is always on top, then the two currencies with largest balances are shown in descending order. This will make more sense when the "all balances" button is added to provide access to the rest of the balances.
When a new transaction occurs the balances are updated.
This PR also contains a html/sass refactor suggested by @wynlim that groups the dashboard elements by column instead of by row. This cleaned up a lot of duplicate class names, and provides a more modular container structure that will allow the balance list to grow longer if needed.

Fixes #657.

![screen shot 2014-08-18 at 4 58 37 pm](https://cloud.githubusercontent.com/assets/3108007/3959783/a4cb118e-2733-11e4-82ae-d4ad3b8a6c18.png)

![screen shot 2014-08-18 at 5 02 18 pm](https://cloud.githubusercontent.com/assets/3108007/3959826/49172bf6-2734-11e4-87ea-88a8c34d0588.png)