OME release job

This PR reimports the scripts from https://gist.github.com/joshmoore/3665755 into the main code and adds more functionality to allow
- to create new release folders and symlink the promoted artifacts
- to generate the downloads pages using the `gen.py` and `bfgen.py

Note: there is still work to do on this PR but I have been able to reproduce a release process locally and opening this PR allows to create an OME-merge-release job on hudson to test it in production.