WandB/Colab + docs

[C-Achard]

This PR is intended to provide wandb integration in napari, as well as a Colab notebook for training.

• [x] WandB for WNet
• [x] WandB for other models ? -> #50

• [ ] WandB parameters in plugin ?

• [x] Minimal Colab notebook

• [x] ZeroCostDL4Mic-style notebook

• [x] Complete WNet training docs
• [x] Add WandB/Colab tutorials and docs

• [x] Fully update all docs -> #50

• [x] Decide for Dice metric : include background or seek best Dice channel ?

[MMathisLab]

looks good, please fix merge conflicts and merge

[C-Achard]

looks good, please fix merge conflicts and merge

Will do, thanks for the review !