:sparkles: Add trajectory models including Snapshot Ensembles

[o-laurent]

• [x] Check for better architectural choices
• [x] Add SWA
• [x] Add EMA
• [x] Add SWAG
• [x] Fix SWAG
• [x] Fix configuration files
• [x] Improve coverage
• [x] Add everything to the documentation
• [ ] Add tutorials
• [x] Enable choosing the postprocessing method in the config files

This PR will close #100.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.06299% with 20 lines in your changes missing coverage. Please review.

Project coverage is 98.21%. Comparing base (e137610) to head (fdbaf76). Report is 5 commits behind head on dev.

Files	Patch %	Lines
torch_uncertainty/models/wrappers/swag.py	90.99%	3 Missing and 7 partials :warning:
torch_uncertainty/routines/classification.py	93.02%	2 Missing and 4 partials :warning:
torch_uncertainty/models/wrappers/stochastic.py	95.00%	1 Missing and 1 partial :warning:
...uncertainty/models/wrappers/checkpoint_ensemble.py	96.55%	0 Missing and 1 partial :warning:
torch_uncertainty/post_processing/laplace.py	96.29%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #101 +/- ## ========================================== - Coverage 98.48% 98.21% -0.27% ========================================== Files 119 127 +8 Lines 5744 6052 +308 Branches 765 819 +54 ========================================== + Hits 5657 5944 +287 - Misses 46 53 +7 - Partials 41 55 +14 ``` | [Flag](https://app.codecov.io/gh/ENSTA-U2IS-AI/torch-uncertainty/pull/101/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS-AI) | Coverage Δ | | |---|---|---| | [cpu](https://app.codecov.io/gh/ENSTA-U2IS-AI/torch-uncertainty/pull/101/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS-AI) | `98.21% <96.06%> (-0.27%)` | :arrow_down: | | [pytest](https://app.codecov.io/gh/ENSTA-U2IS-AI/torch-uncertainty/pull/101/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ENSTA-U2IS-AI) | `98.21% <96.06%> (-0.27%)` | :arrow_down: | 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-AI#carryforward-flags-in-the-pull-request-comment) to find out more.

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