Refactor computation of primitive lists in `DeepFeatureSynthesis` `__init__`

When building the following lists, there is a lot of code duplication:

- `self.groupby_trans_primitives`
- `self.agg_primitives`
- `self.where_primitives`
- `self.trans_primitives`

Furthermore, refactoring this logic outside of the `__init__` would help make the code more expressive and testable.