Fix minor style issues in StockSource/StockWidget

This pull request fixes some minor style issues in StockSource and StockWidget. Most are whitespace-issues, but some unused code is also removed.
@jcazevedo @Bjesus1 What do you think of calling this widget (not the source) `StockListWidget` instead of `StockWidget`? The first stock widget that comes to my mind is something like [this one](http://shopify.github.io/dashing/images/widget2.png) and we may want to create one like that later. Just a suggestion, I don't mind if the name stays as it is right now ;)