Improve appearence of payment option list

Follows neighborly/neighborly-balanced-creditcard#18.

# Before
![screen shot 2014-03-07 at 14 25 09](https://f.cloud.github.com/assets/667753/2359915/75a2ffee-a61d-11e3-9fb0-d10723ad5acd.png)

# After
![screen shot 2014-03-07 at 14 23 07](https://f.cloud.github.com/assets/667753/2359899/464acec0-a61d-11e3-95df-5f49b68e96bb.png)

/cc @snconnolly