Always use the custom change_form_template.

When using the WYSIWYG editor, set a context variable instead.

I had some weird issues when after viewing an item with a WYSIWYG editor, entries with text/plain also showed the WYWSIYG editor until the django server was restarted. Viewing text/plain entries *first*, worked as expected, but as soon as viewing a text/html entry, everything showed the WYSIWYG editor.