title: Is there a file size limit or extension limit in wagtail?
body: <p>I have a very simple model (Product) which is used as an InlinePanel in a page. </p>
  
  <p>Product has a FileField which works fine as long as I upload small files, but as soon as I upload a large file (>5MB), I somehow get an CSRF error. Both on local and on production. </p>
  
  <p>It is not an issue with nginx max upload size.</p>
  
  <p>Is there a file size limit or extension limit in wagtail?</p>