For Cordova boilerplate referenced js urls are always absolute

Should fix a bug that was kinda hard to reproduce but was noticed before:

- open the app that wasn't HCP'd
- change the current url path with HTML5 pushState
- call window.location.reload()
- observe the packages code not being loaded properly
Extract the launch screen logic to a separate package

That can be configured in apps to postpone the launch screen until a certain
moment with some sane default behavior.