Remove GitLFS Dependency

[crvernon]

The GitLFS dependency for this repository has proven to be problematic for many users. However, Xanthos 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 Xanthos >= 2.2.0 releases,
• Built an InstallSupplement class that fetches and unzips the Zenodo example data package into the Xanthos root directory,
• Call the InstallSupplement class after setup has completed in setup.py,
• Removed and replaced any GitLFS archived files that existed within the project,
• Adjusted the paths in the test configuration files to recognize the working directory.

All tests have passed as executed via Travis.

Resolves #38

[crvernon]

I may need to un-init GitLFS to make the dependency actually vanish; though the heavy-lifting in terms of LFS file installation is done. I'll check into this.

[rplzzz]

@crvernon How are we doing on this task? I haven't seen an update in a while.

[crvernon]

Alright @rplzzz we are ready to roll with a review on this one.

• I made the reference data part of the package which is called accordingly
• replaced all __file__ calls with proper package lingo using pkg_resources
• dumped the auto-install of the example data on setup
• removed all GitLFS pointers and objects (see https://github.com/git-lfs/git-lfs/issues/3026)
• set up Travis-CI to install the example data for tests in the travis config outside
• fixed all paths in all tests, etc.

The protocol for installing the example data for Xanthos is now conducted by executing the following after install:

from xanthos import InstallSupplement
InstallSupplement("<path to the directory you wish to store the example data in>")

Once the the current checks have completed - they will pass - you can review. After I get the OK from you, I will add this install protocol to the README (BTW, we need a readthedocs.io page) and mint the new example data for usage with the most recent version.