PDFBOX-2151: Replace log4j with commons logging, as suggested by Simon Steiner; fix imports

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/branches/1.8@1603972 13f79535-47bb-0310-9956-ffa450edef68
PDFBOX-2151: revert commit that doesn't belong

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/branches/1.8@1603976 13f79535-47bb-0310-9956-ffa450edef68