Adding DL models

[jemus42]

The current implementations we have available appear to be too unstable to use --- at least I failed to get deepsurv and deephit running reliably.

Fore completeness, I think we should aim to include at least two of them, but we might have to wait for new implementations, maybe based on {torch} rather than pycox/{survivalmodels}.

[jemus42]

Waiting for sophie & niklas' project on doing exactly that.

Might start the benchmark without them and add them after the fact, but fiddling with existing batchtools registries is always a bit scary.