Add logging for applying rule

lib/models/documents/document.dart

@@ -139,7 +139,6 @@ class Document {
   static Delta _transform(Delta delta) {
     Delta res = Delta();
     for (Operation op in delta.toList()) {
-      // TODO
       res.push(op);
     }
     return res;

lib/models/rules/rule.dart

@@ -62,6 +62,7 @@ class Rules {
       delta =
           rule.apply(delta, index, len: len, data: data, attribute: attribute);
       if (delta != null) {
+        print("Rule $rule applied");
         return delta..trim();
       }
     }