`train_base_command()` is border line too complex according to flake8

While debugging for #419, I had to add some debugging code, not that much and when I tried to commit my changes, `flake8` was complaining that `train_base_command()` was too complex.
We should consider refactoring that function.

```
flake8...................................................................Failed
- hook id: flake8
- exit code: 1

everyvoice/base_cli/helpers.py:147:1: C901 'train_base_command' is too complex (42)
```