IWizardFactory: Create wizards with factoryCreators

Do not use the object pool to hold potential wizards. Register
FactoryCreator functions with IWizardFactory instead and use
those to create the wizards when necessary.

This saves us a couple of cycles during startup since we can now
delay construction of all wizards and it makes us more flexible
wrt. managing the lifecycle of the wizard factories.

Change-Id: I95d6a6dfcdf0fd995e1934a9fefcd96c6a676753
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/coreplugin/icore.cpp

@@ -533,11 +533,6 @@ void ICore::openFiles(const QStringList &arguments, ICore::OpenFilesFlags flags)
     m_mainwindow->openFiles(arguments, flags);
 }
 
-void ICore::emitNewItemsDialogRequested()
-{
-    emit m_instance->newItemsDialogRequested();
-}
-
 void ICore::saveSettings()
 {
     emit m_instance->saveSettingsRequested();