Add 'post as moderator' option for comments.

* Add 'post as moderator' option to comment form. This creates a so-called sticky comment.
* Downvotes have no effect on stickied comments; they're always visible, regardless of comment thresholds.
* Only mods may sticky comments.
* Mods may sticky comments by other users.

app/assets/stylesheets/specific/comments.css.scss

@@ -48,10 +48,6 @@ div.comments-for-post {
       opacity: 1.0;
     }
   }
-
-  div.comment-preview {
-    margin-bottom: 2em;
-  }
 }
 
 div#c-posts {
@@ -146,3 +142,12 @@ div#c-comments {
     }
   }
 }
+
+form.edit_comment div.input.boolean {
+  display: inline-block;
+
+  label {
+    font-weight: normal;
+    vertical-align: initial;
+  }
+}