REF: extract params used in DataFrame.__repr__
`DataFrame.__repr__` used different parameters than `DataFrame.to_string` and I've got a case where I want to use the `__repr__` ones, but with a change to one of the parameters. This refactoring makes it possible to extract those parameters so we can do:

```python
>>> params = pd.io.formats.format.get_frame_repr_params()
>>> params[my_param] = new_value
>>> df.to_string(**params)
```
