fixed image uploading, and display inheader

this is the big reason it wasnt working though, the "is_image_allowed" method is defined in the Form class, not the field. So you should call  ```form.is_image_allowed()``` not ```form.user_avatar.is_image_allowed()``` 
you might have been wanting to pass the field as an argument, which would be 
``` form.is_image_allowed(form.user_avatar)``` but i show eariler in the commit why thats not needed and the correct call should just be ```form.is_image_allowed()```