BitcoinBalance: Increase signal to "medium".

Old one wasn't coming up by default:
![screen shot 2014-06-24 at 9 23 55 pm](https://cloud.githubusercontent.com/assets/81969/3380487/765ddf72-fc07-11e3-8571-63a1b4084bfa.png)

Adding `signal: 'medium'` fixes that:
![screen shot 2014-06-24 at 9 24 03 pm](https://cloud.githubusercontent.com/assets/81969/3380488/765df124-fc07-11e3-834e-d5242731ae7e.png)

https://ddh1.duckduckgo.com/?q=1Gn2dRFqouUHvuWPVhriCDtP3qVQc59WHy