rebaseline_server: improve pixel diff reporting

gm/rebaseline_server/static/view.css

 /* Special alert areas at the top of the page. */
 .todo-div {
     background-color: #bbffbb;
 }
 .warning-div {
     background-color: #ffbb00;
 }
 
 /* Tab which has been selected. */
 .tab-true {
@@ skipping 12 matching lines @@
     display: inline-block;
 }
 /* The main working area (connected to the selected tab). */
 .tab-main {
     background-color: #ccccff;
 }
 
 .update-results-button {
     font-size: 30px;
 }
+
+.image-link {
+    text-decoration: none;
+}