Minor tidying of contributing docs
Redirect Python API documentation to new Sphinx-generated pages

With 5.1.0-m1 the epydoc has been deprecated from the build so the old API
documentation links are obsolete and need to be redirected to the new
Sphinx-generated API documentation. A specific extlink is added to point at
this Python-generated documentation.
Merge pull request #1010 from hflynn/trello-link

Minor tidying of contributing docs
Merge pull request #1011 from sbesson/sphinx-api

Redirect Python API documentation to new Sphinx-generated pages
merge develop -Dnone -Ibreaking -Eexclude -Ssuccess-only

Repository: openmicroscopy/ome-documentation
Excluded PRs:
  # PR 1009 manics 'Update Linux walkthrough to 5.0.5 (rebased onto develop)' (user: manics)
  # PR 990 kennethgillen 'for users who have compiled isapi_wsgi on x64' (user: kennethgillen)
Updating 99514d2..47e3bec
Previously merged:
  # PR 1011 sbesson 'Redirect Python API documentation to new Sphinx-generated pages'
  # PR 1010 hflynn 'Minor tidying of contributing docs'
  # PR 1008 hflynn 'Adding link to secvuln on sysadmin security page (rebased onto develop)'

Generated by OME-5.1-breaking-push#119 (http://ci.openmicroscopy.org/job/OME-5.1-breaking-push/119/)