Drush 10/11 support

I've got this working runs saved by tideways_xhprof, using the latest patch here, but I also had to make a couple more changes:

1) The source=Drush query string parameter doesn't 'stick' around various links in the UI (e.g. when sorting from table headers, or clicking the 'show all' link above the table). So I just temporarily hacked \Drupal\xhprof\Profiler::getNamespace() beyond what the patch did, to just always return 'Drush'.

2) I couldn't see how to set the output directory for tideways_xhprof; it always wrote into /tmp for me. The xhprof.output_dir PHP seems to be ignored (which makes sense, given it's a different extension), and it doesn't seem to use what's returned by sys_get_temp_dir() either. So I had to add arguments: ['/tmp'] to the xhprof.file_storage service definition in xhprof.services.yml .

I doubt these are appropriate changes for everyone, but perhaps a patch could be made to accommodate those in my position too? Unless it's literally only me! :-D