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
Please check here http://www.openmicroscopy.org/site/support/omero5-staging/sysadmins/server-ldap.html#ldap-properties