[dev] Config Registration Functions in __init__.py

[romesco]

implements config registration for optim via __init__.py

If this looks good, I'll broadcast the same strategy across the rest of the configs we currently have.

Partially Addressing #53

[romesco]

Before merging, I just want to point out that because of the way pytorch structures its files (and __init__.py for certain modules), the optimizer register can be done like this:

hydra_configs.torch.optim.register()

however, losses and data-related must be done like this:

hydra_configs.torch.nn.modules.register()
hydra_configs.torch.utils.data.register()

For now it's not possible to do:

hydra_configs.torch.nn.modules.loss.register()

because loss.py is an auto-generated file and we aren't putting logic in those.

Semantically, registering optimizers with optim.register() is nicer than the case for loss which is registered by modules.register().

I'm open to ideas for ameliorating this semantic ambiguity.