title: django one widget for two m2m fields
body: <p>I have two manytomany fields for my model ModelFrom, that both go to the same Model, call it ModelTo.</p>
  <pre><code>ModelFrom(models.Model):
      field_one = ManyToManyField(ModelTo)
      checked = ManyToManyField(ModelTo)
  </code></pre>
  <p>checked is a subset of field one. I have properly validated this in model clean() and adminform clean() methods, and updated model::save() to call self.full_clean().</p>
  <p>Ideally, I would have one widget, much like the django.forms.SelectMultiple, but with a checkbox inside each <code>&lt;option&gt;</code>.</p>
  <p>what it currently looks like, I have one of these widgets for each field:
  <img src="https://i.stack.imgur.com/MAGR4.png" alt="current look" />:</p>
  <p>I want to combine them and have a checkbox or something, here is my unicode representation of what it would look like</p>
  <p>{  [ blah: 2 ☐] , [blah: 1 ☑] }</p>
  <p>Value in the list -&gt; field one is set. Checked box -&gt; checked is set as it is a subset of field_one.</p>
  <p>I have seen jQuery UI MultiSelect Widget but there doesn't seem to be a way to be able to select an option, but not check the box.</p>