Alert users w/o JavaScript about its need when completing contributions

One of [Balanced](https://www.balancedpayments.com/)'s steps to complete payment transaction is done via JavaScript. Telling the users about this need would be really cool.

# With JavaScript enabled
![screen shot 2014-02-20 at 12 04 09](https://f.cloud.github.com/assets/667753/2219441/b2e6cbda-9a40-11e3-95c9-ce1b6872c3af.png)

# Without JavaScript enabled
![screen shot 2014-02-20 at 12 08 22](https://f.cloud.github.com/assets/667753/2219462/e4cf1efe-9a40-11e3-9d2b-81b79a01bd51.png)