Switch to JavaScriptEngineSwitcher 2.0

[Daniel15]

See https://github.com/Taritsyn/JavaScriptEngineSwitcher/wiki/How-to-upgrade-applications-to-version-2.X for list of changes. Notably, we should remove the JS engines from the ReactJS.NET dependency injection container in favour of using the standard JavaScriptEngineSwitcher config classes.