Add link to the new form

[MAILPOET-1798]

assets/css/src/components/_postEditorBlock.scss

@@ -1,6 +1,8 @@
 .mailpoet-block-div {
-  background: #cfc;
-  border: 2px solid #9c9;
-  color: green;
   padding: 20px;
 }
+
+.mailpoet-block-create-new-content {
+  display: flex;
+  flex-direction: column;
+}

assets/js/src/post_editor_block/edit.jsx

@@ -19,6 +19,7 @@ function Edit({ attributes, setAttributes }) {
             selectedForm: parseInt(event.target.value, 10),
           });
         }}
+        className="mailpoet-block-create-forms-list"
         defaultValue={attributes.selectedForm}
       >
         <option value="" disabled selected>Select a MailPoet form</option>
@@ -45,11 +46,20 @@ function Edit({ attributes, setAttributes }) {
       {
         attributes.selectedForm === null && (
           <Placeholder
-            className="mailpoet-block-div"
+            className="mailpoet-block-create-new"
             icon={<BlockIcon icon={Icon} showColors />}
             label="MailPoet Subscription Form"
           >
+            <div className="mailpoet-block-create-new-content">
+              <a
+                href="admin.php?page=mailpoet-forms"
+                target="_blank"
+                className="mailpoet-block-create-new-link"
+              >
+                Create a new form
+              </a>
               {displayFormsSelect()}
+            </div>
           </Placeholder>
         )
       }