static-fe: don’t squeeze non-square emoji

Emoji and the navbar items want to let blend in with lines of text,
so fix their height and let the width adjust as needed.

priv/static/static-fe/static-fe.css

@@ -117,6 +117,7 @@ nav {
 
 .inner-nav img {
     height: 28px;
+    width: auto;
     vertical-align: middle;
     padding-right: 5px
 }
@@ -642,13 +643,13 @@ summary {
 }
 
 img:not(.u-photo, .fa-icon) {
-    width: 32px;
+    width: auto;
     height: 32px;
     padding: 0;
     vertical-align: middle;
 }
 
 .username img:not(.u-photo) {
-    width: 16px;
+    width: auto;
     height: 16px;
 }