Add ModelBase configuration option to force strict update by default

[dgilland]

In ModelBase.update() there is an argument to restrict updatable fields to Model.strict_update_fields. By default, strict update is disabled when calling update() and requires update(..., strict=True) to enable. A configuration property should be available to make strict=True the default. Something like ModelBase.__strict_update__ = False and update(..., strict=None).

[dgilland]

Considering removing the strict update concept and requiring this to be implemented in user-land.