Migrate service/application discovery mechanism to Spring Boot 2.x/Spring Cloud Hoxton

[punycode]

While talking with @derTobsch, we decided to not change up too much. The existing issue #59 for replacing the Eureka-based service discovery will therefore be put onto the back burner and migrate the existing Spring Cloud Eureka implementation to the current Spring Cloud stack.

This will allow us to also learn about the parts that are currently tied to Eureka in the first place. Abstracting over those will then help adding support for alternatives later on.