Added icon to preferences option in tool menu
Added icon to preferences option in tool menu

martinra/geary,glebihan/geary,glebihan/geary,dominickm/Geary,orlandosanchez/geary,MohamedIM/geary-unofficial,abn/geary,AtticHacker/geary,AtticHacker/geary,rschroll/geary,kyoushuu/geary,mjog/geary,aatishnn/geary,kyoushuu/geary,dominickm/Geary,aatishnn/geary,githubnemo/geary,geekvigilante/geary,robol/geary,emersion/geary,jimbonator/geary,aatishnn/geary,didrocks/geary,tshikaboom/geary,rschroll/geary,tshikaboom/geary,jimbonator/geary,orlandosanchez/geary,emersion/geary,githubnemo/geary,tshikaboom/geary,mjog/geary,robol/geary,martinra/geary,mjog/geary,glebihan/geary,githubnemo/geary,kpiwko/geary,AtticHacker/geary,jimbonator/geary,martinra/geary,mpdeimos/geary,emersion/geary,orlandosanchez/geary,robol/geary