Add Preboot

[Splaktar]

Based on the discussion in these issues

• Cannot find a way to achieve a smooth transition to client app angular/universal#1184
• Using platform server, lazy loaded component flickers as the browser renders the application angular/angular#15716

It appears that Preboot is required to avoid page flickering when using SSR with apps that have a moderate amount of content and use lazy loaded routes.

angular/universal#1184 (comment) has an example of implementing Preboot and links to a repo that has an implementation that solves this.

Additionally initialNavigation: 'enabled' is a required part of fixing these flicker issues, that's been done in 9f1fc47.