Do not force square affiliation logos

According to the spec, they should be 64x64. We warn on import if they
are not, but if we import different sized icons they get stretched.
Instead, assume logos of at least 32px in width OR 32px in height and
scale them such they are contained in the defined 32x32px reserved
space.

Author: Kevinjil

webapp/public/style_domjudge.css

@@ -236,8 +236,8 @@ del {
 }
 
 img.affiliation-logo {
-    height: 32px;
-    width: 32px;
+    max-height: 32px;
+    max-width: 32px;
     padding-left: 2px;
 }