readthedocs: missing configuration property hyperlinks

[sbesson]

Since the migration to readthedocs, it looks like the property Sphinx directive which used to refer to the relevant section within the configuration glossary page is partly broken.

Compare for instance omero.web.login_logo on the following pages:

https://docs.openmicroscopy.org/omero/5.6.4/sysadmins/customization.html#login-page-logo

vs

https://omero.readthedocs.io/en/v5.6.7/sysadmins/customization.html#login-page-logo