factor out asyncLoader from simLauncher, https://github.com/phetsims/tambo/issues/126 https://github.com/phetsims/joist/issues/687
factor out asyncLoader from simLauncher, https://github.com/phetsims/tambo/issues/126 https://github.com/phetsims/joist/issues/687

phetsims/phet-core,phetsims/phet-core,phetsims/phet-core