Minor tidying.

Disable some new 'controversial' PMD rules, and enable some of the
others we had suppressed.

Change-Id: Ia15d78858617e8b4dcc71c47b91d9975118206a9
Reviewed-on: http://gerrit.dmdirc.com/3642
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>