Show warning/error in Build time if subprocesses contains any Start Event but None

According to BPMN 2.0 specification all subprocesses (except Event Subprocess) can contain only None Start Event.

Now it is possible to place different types of Start Event inside of Suprocesses (like Embedded Subprocess) and no warnings/errors will be raised during building time. At runtime Starts Events will behave as None Start Events and specific Start Event Type will be ignored.

For more details see BPMN 2.0 specification page 241 at the bottom.