Refactor `morphoclass morphometrics` CLI + Fix SSH

[FrancescoCasalegno]

Fixes #60

Description

1. morphoclass morphometrics extract-features now takes in input the dataset-csv (i.e. only one CSV file) instead of organised-dataset-directory (i.e. a whole directory that is then explored to read CSV files for each layer). This makes the command more similar to morphoclass extract-features.
2. The output filesystem structure produced of feature extraction and model training is now the same for morphoclass and other features. I.e. the naming convention follows the structure <dataset>-<layer>:

   extract-features-morphometrics/
   ├── in-L1
   ├── in-L23
   ├── in-L4
   ├── in-L5
   ├── in-L6
   ├── in-merged
   ├── in-merged-bc-merged
   ├── janelia-L5
   ├── pc-L2
   ├── pc-L3
   ├── pc-L4
   ├── pc-L5
   └── pc-L6

3. Enable SSH: replace dvc by dvc[ssh] in requirements-extras.txt + add apt-get install ssh in the Dockerfile.

Checklist

• [x] This PR refers to an issue from the issue tracker. (if it is not the case, please create an issue first).
• [x] setup.cfg, requirements.txt, and constraints.txt updated with new dependencies. (if needed)
• [x] All CI tests pass.