Remote load of example data

[philerooski]

Currently, the majority of the package's size comes from the example datasets. Rather than including the data with the package, we should include functions for easily fetching the data from a remote server.

It's possible this will only be feasible once oAuth is implemented on Synapse, sometime in late 2019. We can include oAuth tokens with the package giving users programmatic access to the file handles of the example datasets.

Sample data loading is already done this way in Keras. See, for example, keras.datasets.cifar10.load_data.