✨ Sparsification metric and plot methods for Calibration Error

[alafage]

• [x] Add Sparsification Error from Ilg et al., Uncertainty estimates and multi-hypotheses for optical flow. In ECCV, 2018.
• [x] Create wrapper classes for BinaryCalibrationError and MulticlassCalibrationError to provide plotting methods.
• [x] Write Tests
• [x] Update Documentation
• [x] Update the calibration tutorial

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (bfbae6b) 98.36% compared to head (9cb2200) 98.39%.

Files	Patch %	Lines
torch_uncertainty/routines/classification.py	80.00%	0 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #68 +/- ## ========================================== + Coverage 98.36% 98.39% +0.03% ========================================== Files 74 76 +2 Lines 3792 3874 +82 Branches 473 473 ========================================== + Hits 3730 3812 +82 Misses 26 26 Partials 36 36 ``` | [Flag](https://app.codecov.io/gh/ENSTA-U2IS/torch-uncertainty/pull/68/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS) | Coverage Δ | | |---|---|---| | [cpu](https://app.codecov.io/gh/ENSTA-U2IS/torch-uncertainty/pull/68/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS) | `98.39% <98.57%> (+0.03%)` | :arrow_up: | | [pytest](https://app.codecov.io/gh/ENSTA-U2IS/torch-uncertainty/pull/68/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS) | `98.39% <98.57%> (+0.03%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS#carryforward-flags-in-the-pull-request-comment) to find out more.

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[o-laurent]

Does #69 take precedence to test the workflows in passing?