Handle changes made to the Application.myapp file in disk.

[melytc]

I need to validate with @tmeschter how to handle external changes using DocData. Right now, the current implementation is not aware of external changes.

Related #8252.

[melytc]

@kvenkatrajan this is not addressed yet: the myapp file detects when a property has changed and refreshes their values, but the UI does not reflect the changes.