SonarQube badge needs updated link

[hansjoachim]

The link to the SonarQube project in the README.md (http://nemo.sonarqube.org/dashboard/index?id=org.fitnesse%3Afitnesse) is currently failing. Looks like the server has shuffled around a bit and dropped the nemo-subdomain, because https://sonarqube.com/dashboard/index?id=org.fitnesse%3Afitnesse works.

I am not sure how this is set up though, and it looks like the image with tech debt percentage is still loaded, but I don't know where it gets the number from.

(Btw, think I saw some default interface implementations, has the source code moved to Java8? Should SonarQube be configured to check against Java-8 ruleset?)