Extract project archive contents to gh-pages

[jlstevens]

This is needed for instance in the updated attractors project which now refers to a .py file in the project. For relative links to work to these assets, the project should be extracted to the correct directory on gh-pages: this should be fine as the projects should always be small (e.g we are not allowing large data files to be committed with projects). This would also allow you to link to the corresponding anaconda-project.yml for instance.