PDFBOX-1966: Type 1, 4 and 5 shadings for shFill(); use transparency for type 6 and 7; DRY principle will be applied later

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/branches/1.8@1575539 13f79535-47bb-0310-9956-ffa450edef68