Quiet option for gmclash

Hi @mbandier,

Would it be possible to add a "quiet" option for gmclash, to suppress the messages like

*************  Checking overlaps for volume av_64230_impr_1_StaveCylHatFoot0_pv_4_StaveCylHatFoot0 (G4Tubs) ... OK, done! 

and only print messages when a clash is detected? For detectors with a lot of volumes (like the ITkStrip) I suspect that printing so many messages is contributing non-negligibly to the total time overhead, and it also makes the console output more-or-less useless, as it is impossible to find any clashes among the "standard" messages. Of course, one can check the json file, but the console output is a bit more informative often.

Thanks,

Nick.