add support to blacklist clipboard windows by wm_class
add support to blacklist clipboard windows by wm_class

not all clipboard windows have wm_class(or other useful props),
the one i need does(keepassx)

aniruddhkanojia/qtile,soulchainer/qtile,xplv/qtile,zordsdavini/qtile,kopchik/qtile,encukou/qtile,andrewyoung1991/qtile,soulchainer/qtile,qtile/qtile,frostidaho/qtile,EndPointCorp/qtile,farebord/qtile,flacjacket/qtile,dequis/qtile,tych0/qtile,tych0/qtile,kseistrup/qtile,encukou/qtile,nxnfufunezn/qtile,andrewyoung1991/qtile,ramnes/qtile,w1ndy/qtile,kynikos/qtile,kseistrup/qtile,himaaaatti/qtile,kopchik/qtile,de-vri-es/qtile,kynikos/qtile,xplv/qtile,himaaaatti/qtile,StephenBarnes/qtile,rxcomm/qtile,ramnes/qtile,rxcomm/qtile,apinsard/qtile,zordsdavini/qtile,jdowner/qtile,StephenBarnes/qtile,farebord/qtile,de-vri-es/qtile,nxnfufunezn/qtile,flacjacket/qtile,qtile/qtile,apinsard/qtile,w1ndy/qtile,aniruddhkanojia/qtile,cortesi/qtile,EndPointCorp/qtile,kiniou/qtile,jdowner/qtile,frostidaho/qtile,cortesi/qtile,kiniou/qtile,dequis/qtile