create end-to-end sgoop example w/o large data files

[anotherjoshsmith]

According to the scientific-python-cookiecutter, large files should never enter your git repo. I haven't seen a big performance dip with git unless i'm actively uploading/downloading files in a commit... but figure it's better to find a new way to generate examples. Perhaps a separate cookiecutter-sgoop-example repo would be a good way to allow new users to play around with SGOOP with Plumed and GROMACS. In the current repo, the model potentials might be an effective way to demonstrate SGOOP in the absence of MD.

• add alanine dipeptide example in separate repo
• add model potential example in this repo

[anotherjoshsmith]

Model potential examples added in #10. Could stand to make these more like tutorials in the future.