* add contrast to conf/class against bbox rectangle color

* added feature to save conf in txt labels

* Update general.py

* Update detect.py

* Update detect.py

* Update detect.py

save_conf variable removed as only used once, so we can use opt.save_conf instead.

* Update detect.py

* Update detect.py
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>