Spree 2.x styling for product dropdown

This patch updates the New Issue view to Spree 2.x styling, which adds nice autocompletion to the product name and converts this view:

![screen shot 2014-08-04 at 3 45 33 pm](https://cloud.githubusercontent.com/assets/2460418/3804628/24142a9a-1c29-11e4-9917-a04ed97a9c09.png)


To this view:


![screen shot 2014-08-04 at 3 45 06 pm](https://cloud.githubusercontent.com/assets/2460418/3804629/27566844-1c29-11e4-84b5-9a34eb6da126.png)