PDME — PDM RTF issue: no generic "set session properties" operation

This new JCAD issue looks to apply equally well to PDM Enablers.
We might want to add an operation like

PdmSystem::set_session_properties (
in CosPropertyService::Properties session_properties
) raises (PDM_EXCEPTIONS,
PdmFoundation::InvalidProperties,
PdmFoundation::CannotChangeWithoutReconnect);

A matching get_properties operation may not be needed if everyone
thinks that this would be redundant with PdmServer::get_properties.