Add Stanford University seal as first footer logo

Three logos now: Stanford University -> biochemistry.stanford.edu
parent (Stanford Medicine | Biochemistry) -> HHMI. New PNG cropped
to content (1998x469 -> 1834x305) and rendered at height: 30px to
match the others.

Author: rhiju

_includes/footer.html

@@ -4,6 +4,9 @@
     <div class="footer-bar-teal"></div>
   </div>
   <div class="institutional-logos">
+    <a href="https://www.stanford.edu/" target="_blank" rel="noopener noreferrer external">
+      <img class="logo-stanford-university" src="{{ '/assets/images/site/public/nav_logo_stanford_university.png' | relative_url }}" alt="Stanford University">
+    </a>
     <a href="https://biochemistry.stanford.edu/" target="_blank" rel="noopener noreferrer external">
       <img class="logo-stanford-medicine" src="{{ '/assets/images/site/public/nav_logo_stanford_medicine.png' | relative_url }}" alt="Stanford Medicine — Biochemistry">
     </a>

assets/css/style.scss

@@ -783,6 +783,7 @@ details.show-more {
     &:hover { opacity: 1; }
   }
 
-  .logo-stanford-medicine { height: 30px; }
-  .logo-hhmi              { height: 30px; }
+  .logo-stanford-university { height: 30px; }
+  .logo-stanford-medicine   { height: 30px; }
+  .logo-hhmi                { height: 30px; }
 }