• This PR closes [core] Enable / update dogfood ruleset on PMD's codebase #361 (We'll continue to update the dogfood ruleset as needed)
• It deletes the old dogfood rulesets.
• The maven profile "jdk8-modules" is gone now - all modules are enabled by default. We are enforcing java9 for building PMD, so we can simply enable always all modules. This should make it easier to import PMD into IDEA/eclipse

btw.: I'll probably release PMD 6.2.0 Monday morning (CEST).