Updates

Allow easy access to the datasets held by the DataModule. Previously there was no direct way of accessing them without having to go through the private members of the DataModule. This complicated certain cases where the length of the dataset was required.
Added a way to halt training based on arbitrary conditions. The main use-case for this is to allow the Model sub-classes to halt training when the trained network has converged to a value or if the network is diverging and there's no reason to continue.
Addresses a potential crash that occurs whenever training occurs on a None checkpoint path.

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