Add main document launch support

Main document is an invisble document, so the Runtime class is modified to
support create a Runtime without native app window. The
Runtime::CreateWithDefaultWindow() static function now works like the previous
Runtime::Create() function, a default native app window will bind to the created
Runtime.

So different from local path launch, the main document launch will use
Runtime::Create() to create an invisible runtime. Currently we support both
launch from main document and local path, however the local path launch support
may be deprecated in the future.