Enable a few more PMD rules
I did one last pass over https://pmd.github.io/pmd-5.4.1/pmd-java/rules/index.html and these are the only sane rules left that I could find.
So I'm pretty much done with adding PMD stuff :) Don't know if anyone feels strongly in favour of adding findbugs, but I think checkstyle+PMD is good for now.