404 on default user image in nav bar

the default image for the user in the navbar was returning 404

![screen shot 2013-12-13 at 4 41 43 pm](https://f.cloud.github.com/assets/196181/1740103/f76ed87c-63ba-11e3-80b5-8a95aad01657.png)

fixed by changing navbar template to point to shared asset correctly.