Add donation banner

look/fsfe.less

@@ -130,8 +130,7 @@ img.signatory-logo {
                 padding-top: 1.8em;
             }
             p.text {
-                background-color: rgba(0,0,0,0.5); 
-                background-size: contain;
+                background-color: rgba(0,0,0,0.5);
                 -moz-hyphens: manual;
                 -webkit-hyphens: manual;
                 hyphens: manual;