apply version-based ordering to downloads and change log

This was motivated by seeing the unordered list of old versions of eXide available for download from http://demo.exist-db.org/exist/apps/public-repo/packages/eXide.html: 1.0.7, 2.0.1, 2.0, 1.0.13, 1.0.8, 1.0.15, 1.0.14, 1.0.9, 1.0.11, 1.0.12, 1.0.10.  I realize that the sorting in this commit is naive - treating the entire version as a string, instead of parsing and sorting each number.  But this is a step forward.