Remove old test metrics function

Add processing stats

# Conflicts:
#	bin/kaldi/extract_xvectors.py

+ Download eval dataset
+ Eval script on other voxceleb tasks (-O-clean, -H-clean...)
+ add CONTRIBUTORS.md
+ suppress s3prl warning on other ssl model (but keep warning for wavlm)
+ test custom python loaded model
+ add scoring.sh file to easy score voxceleb tasks

Fix minor bug in sidekit test files creation