add sonar-runner default properties for applied jacoco plugin to userguide

+review REVIEW-5198
fix sonarRunner id in plugins DSL

+review REVIEW-5198
some more details about sonar system properties added to userguide

+review REVIEW-5198
add SonarRunnerRootExtension#forkOptions(Action<? super JavaForkOptions>) to DSL reference

+review REVIEW-5198
Some more tweaks to the sonarRunner userguide chapter

+review REVIEW-5198
minor sonar runner doc tweak

+review REVIEW-5198