More options to lookup parameter files

See Service::getParamFile inside SilecsService.cpp

Currently, parameter files are searched near the binary and inside ./../../../generated-silecs/client/.

(And on two CERN-only locations .. these can be dropped)

For the current systemd setup on frontends, this is not sufficient. Instead, it should be possible to pass a param-file lookup path to silecs, so that parameter files are searched in a foreign folder.