move pretty print metadata key sorter into standalone class

git-svn-id: https://svn.apache.org/repos/asf/tika/trunk@1633845 13f79535-47bb-0310-9956-ffa450edef68
move pretty print metadata key sorter into standalone class, with added PrettyMetadataKeyComparator...argh

git-svn-id: https://svn.apache.org/repos/asf/tika/trunk@1633846 13f79535-47bb-0310-9956-ffa450edef68