Upstream Spyne crashes on POST requests to the HTTP/RPC+JSON webservice.
We patched it in a rather hacky way.

This was a regression from the old codebase, where we installed Spyne
separately from our LUMC GitHub mirror. This is now also referenced in
the requirements.txt file.

Thanks to Ken Doig for reporting the issue.

This is quite a large commit, touching many things related to developer
documentation. It is all focussed on getting as much of this as possible
into the new Sphinx-based documentation.

Some highlights:

- Start Sphinx-based developer documentation, including fairly complete
  instructions for installation and configuration.
- Remove epydoc API docs.
- Rework some docstrings to conform to reStructuredText, so they can be
  used in the API docs generated by Sphinx.
- Move all of the top-level text files to reStructuredText so they can
  linked from the Sphinx-based docs and for consistency.
- Remove many obsolete things from the extras/ directory, including old
  installation scripts and migrations.

Many of the installation related documentation and scripts are removed
or adapted in light of the new automated deployment using Ansible.