Design and implement a mechanism to download datasets from places like github

[anupamamurthi]

Similar to issues: https://github.com/Trusted-AI/AIF360/issues/341 https://github.com/Trusted-AI/AIF360/issues/342

Goal is to have a simple way to download data from github - there are a few repo's that have "processed data" and we may want to easily grab the data automatically

This will make it easy for users to simply use a CLI or python script and grab the data without having to manually download it

Recommendation is to implement a GithubStore? (or something similar)

Please refer to #341 to learn about how to get started, why we care, possible implementation strategy etc

[ashnakhetan]

would love to take a stab at this one!