add motd schema and motd editor

data/static/js/babycode-editor.js

@@ -147,13 +147,17 @@
     if (markup === "" || markup === previousMarkup) {
       return;
     }
+    const bannedTags = JSON.parse(document.getElementById('babycode-banned-tags').value);
     previousMarkup = markup;
       const req = await fetch(previewEndpoint, {
         method: "POST",
         headers: {
           "Content-Type": "application/json",
         },
-        body: JSON.stringify({markup: markup})
+        body: JSON.stringify({
+          markup: markup,
+          banned_tags: bannedTags,
+        })
       })
       if (!req.ok) {
         switch (req.status) {