Move app entry point

Moving the app entry point. We are trying to measure the delay between the app beginning, and a component finishing. But currently, the app starts quite late.

Any resource that is in the document, rather than added to the doc through js, is more likely to be look-ahead-loaded by the preloader.

Surprisingly, it looks like async scripts execute later than defer script; the definition of the script execution ordering could permit that.

Pre-empting through subresources aren't reliable right now, they cause a duplicate resource call.

Browser support seemed fine for this change, but it's pretty tough to perf-test until prod...