Improve usability of "Payment info" page

## Before
![screen shot 2014-10-09 at 3 09 38 pm](https://cloud.githubusercontent.com/assets/667753/4581377/7c30610a-4fdf-11e4-8f67-05017774d016.png)

## After
![screen shot 2014-10-09 at 3 01 09 pm](https://cloud.githubusercontent.com/assets/667753/4581358/54911f5e-4fdf-11e4-9224-3016c87a9afe.png)

Two changes made: set inputs as disabled (which also changes colors) and autoselect current bank account info.

Closes #719.

@snconnolly