Codacy looks for ruleset.xml, so give it what it wants.
Bump PMD version to the one used by Codacy, for consistency.

Change-Id: I3665cac8af833da793ca418953d934cc3a333459
Depends-On: I348b37a14097439f8a56b0a671794410e46201ca
Depends-On: Ifc4aa601de14ca2526646f499f60329ed7c5935e
Reviewed-on: http://gerrit.dmdirc.com/3939
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>

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>

This was previously all under checkstyle/ which is weird as there's
a whole bunch of non-checkstyle stuff. Move everything into the nice
etc/ folder to keep it out of the way and sanely organised.

Change-Id: I0df52e8eddc6588c775a5173b624144807f1e59a
Reviewed-on: http://gerrit.dmdirc.com/3102
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>