Replaces footer icon and margin changes

Closes #602 

* Replaces SUL icon in footer with stacked logo
* Removed left margins for SUL footer and SU footer to align with rest of the site

@jvine Removed left margin for SU logo to align with SearchWorks margin. Please let me know if you want to revert this change

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![image](https://cloud.githubusercontent.com/assets/302258/3805140/70b44544-1c31-11e4-9d41-9c8dfb7c216d.png)