added a healthcheck with caching

Added a healthcheck to make sure the prerenderer is running well.
I decided to render a simple page that uses ui-routing (because it is really important that that really works for SEO)

@Magnetme/developers ready for review
This is not necessary at all: the parent and child process can communicate directly with each other. Hence, the child process should simply notify the parent process when something goes wrong, and the parent process should act accordingly. So the healtcheck resource should just be a resource that always returns 200.