Properties and children become stateful in projectors

[agubler]

Bug

For all widgets in the widget tree properties and children are "reset" to the the object provided to w with widget render, this is not true for widgets that have been converted to a projector using the ProjectorMixin.

Both the properties and children become stateful as the original user defined properties are never re-passed via setProperties or setChildren and as a result this can cause unexpected/inconsistent behaviour.

Any projector should reset it's properties and children to a copy of the last values passed to either setProperties or setChildren before the render - The beforeRender lifecycle hook should provide a mechanism to do achieve this.