Instance-specific registration

In order to support being able to register multiple instances of the same application running, I have changed the registration from using the ID to using the spring.application.name property. This required changing a lot of places that were previously using the ID as the unique identifier.

Additionally, the client URL is now also displayed on the main page, as I think this is important for environments across multiple servers, which multi-instance applications usually run across multiple servers.
As I mentioned on the issue I opened, this makes the table of applications on the main page cluttered.

I am admittedly not 100% happy with this solution, but it does work. Perhaps it would be better to use a different property other than spring.application.name as it is not entirely intuitive that this should be different for different instances of the same application. Maybe a new property like info.instance.name would be better...?

Please discuss and let me know, or if you are happy with it, please feel free to merge this.