Add support for Buefy autocomplete; several other form tweaks

at least the Edit User form should work now, for instance

tailbone/forms/core.py

@@ -760,6 +760,29 @@ class Form(object):
         context['render_field_readonly'] = self.render_field_readonly
         return render(template, context)
 
+    def get_vuejs_model_value(self, field):
+        """
+        This method must return "raw" JS which will be assigned as the initial
+        model value for the given field.  This JS will be written as part of
+        the overall response, to be interpreted on the client side.
+        """
+        if isinstance(field.schema.typ, colander.Date):
+            # TODO: don't recall why "always null" here?
+            return 'null'
+
+        if isinstance(field.schema.typ, deform.FileData):
+            # TODO: don't recall why "always null" here?
+            return 'null'
+
+        if isinstance(field.schema.typ, colander.Set):
+            if field.cstruct is colander.null:
+                return '[]'
+
+        if field.cstruct is colander.null:
+            return 'null'
+
+        return json.dumps(field.cstruct)
+
     def messages_json(self, messages):
         dump = json.dumps(messages)
         dump = dump.replace("'", ''')