OMERO configuration properties

This PR :
- reviews the source code links to `et/comero.properties` across the documentation
- replaces them by links to the `sysadmins/config` page whenever appropriate
- review all references to the server configuration properties and uses the `:term:` markup when possible
The line below is refering to this section via ``:ref:`ldap_configuration` ``. Maybe I should combine these lines?