Change model name following new naming convention

Naming convention can be found here: https://github.com/ivadomed/ivadomed/wiki/repositories

This name change will take place after models are re-trained using ivadomed. The specific fields for the name will look like this:

```
Fields:
- task = seg
- animal = rat
- region = spinal cord
- contrast = ?
- architecture = unet2d ?
```

related to ivadomed/ivadomed#305