PIVOT-689, set the same transparency color already used in Sheets (and other popups) even in Alerts, Dialogs, Palette.
Later check if add a new style property to set backgroundTransparency (and use a new utility method to set transparency on a given color).


git-svn-id: https://svn.apache.org/repos/asf/pivot/trunk@1615694 13f79535-47bb-0310-9956-ffa450edef68