DropDown: Add 'open' class to _node instead of _dropDownNode
DropDown: Add 'open' class to _node instead of _dropDownNode

This makes it feasible to add alternate styles for the drop-down's label
when the drop-down is open.

QuinntyneBrown/mayhem,QuinntyneBrown/mayhem,SitePen/mayhem,QuinntyneBrown/mayhem,SitePen/mayhem,QuinntyneBrown/mayhem,jkieboom/mayhem,SitePen/mayhem,jessevdk/mayhem,jessevdk/mayhem,jkieboom/mayhem,jessevdk/mayhem,jessevdk/mayhem,SitePen/mayhem,jkieboom/mayhem,jkieboom/mayhem