Make save friendlier

• Keep comment save button disabled until actually changed
• Add a "Saved" message flash after save occurs

resources/css/widget.less

 :root {
   --rankedchoice--widget--gap: 1em;
+  --rankedchoice--widget--comment--gap: ~"calc(var(--rankedchoice--widget--gap) / 2)";
+  --rankedchoice--widget--message--color: #666;
 }
 
 .rankedchoice--widget {
@@ -20,10 +22,16 @@
   .comment-form {
     display: flex;
     flex-direction: column;
-    gap: ~"calc(var(--rankedchoice--widget--gap) / 2)";
+    gap: var(--rankedchoice--widget--comment--gap);
   }
 
   .comment {
     min-height: 10em;
   }
+
+  .message {
+    font-size: 0.9em;
+    color: var(--rankedchoice--widget--message--color);
+    margin-left: var(--rankedchoice--widget--comment--gap);
+  }
 }