Consider adding the titanic dataset

It would be nice to have the titanic dataset that we use in our examples ([link](https://github.com/dwave-examples/mutual-information-feature-selection), [link](https://github.com/dwave-examples/feature-selection-cqm), [link](https://github.com/dwave-examples/feature-selection-notebook)), available in code. Something like
```python
from dwave.plugins.sklearn.datasets import load_titanic
```
to mirror [scikit-learn's datasets](https://scikit-learn.org/stable/datasets/toy_dataset.html#iris-dataset)