passing through the factory in order not to use explicitly the type.

This fixes ROOT-9664

in ROOT6 there is only one kind of reflection information. For this
reason, also the neighbouring references to Reflex have been removed.

Only this method will wait configured time for completion wait function.
WebWindow::WaitFor() does not have timeout option

Instead of using static variables just configure gEnv->SetValue()
parameters directly. Adjust tutorial

Always use mutex to protect vector of canvases 

This method is thread safe