title: How to create custom block in wagtail?
body: <p>This is my <code>StreamField</code>:</p>
  
  <pre><code>body = StreamField([
      ('heading', blocks.CharBlock(classname="full title")),
      ('paragraph', blocks.RichTextBlock()),
      ('image', ImageChooserBlock()),
  ])
  </code></pre>
  
  <p>And my question is: how to add my own Block that I can pass to <code>StreamField</code>? I meant block that contains multiple images, something like block? I didn't find answer for my question in wagtail docs.</p>