Mljar-supervised

Fixes matplotlib backend initialization in notebooks after AutoML training 785

Fixes
- fixed issues with new sklearn API 789, 788, 787
- setup matplotlib backend for AutoML and switch it back to original 785

Fixes
- a lot of warning and bug fixes done in 777, 771, 762, 761, 760, 759, 758, 757, 756, 755, 754, 753, 752, 751, 750, 749, 743, 742, 733

🍁 Autumn release created thanks to amazing work of maciekmalachowski, a-szulc, Marchlak :rocket: Thank you :1st_place_medal:

Fix warnings due to packages update.

Fixes
- (380) disable boost on errors step for custom strategy
- (728) fix accuracy metric for Lightgbm

Fixes
- (725) fix styling of AutoML report, apply styles in the `mljar-automl-report` class