Remove GitLFS and add InstallSupplement

[crvernon]

The GitLFS dependency for this repository has proven to be problematic for many users. However, CERF still has the need to include larger files as an example directory. To solve this issue I completed the following:

• Zipped the existing example directory and minted a DOI for it using Zenodo that establishes a supplemental data package for the releases,
• Built an InstallSupplement class that fetches and unzips the Zenodo example data package into a directory of the users choosing,
• Removed and replaced any GitLFS archived files that existed within the project.

This can be used in the following way:

from cerf import InstallSupplement

InstallSupplement('<user specified path>')