Save/load hyperparameters with checkpoint
Right now, test tube users can have model.load_from_metrics, but there's no equivalent functionality for users of other logging frameworks. I believe we discussed a while ago that this functionality should be decoupled from logggers.
Proposal:

When hyperparameters are stored as an argparse.Namespace in the hparams property of the model (as already required to get automatic hyperparam logging), save these parameters as part of checkpoints.
Add a load_from_checkpoint classmethod to LightningModule that basically duplicates the functionality of load_from_metrics, but gets the hyperparameters from the checkpoint directly.

I'm happy to send a PR if this proposal looks okay.