Augsburg GR notebooks

[gertingold]

• [x] Cover.ipynb
• [ ] IntroductionGravipy.ipynb
• [ ] SchwarzschildMetric.ipynb
• [ ] EddingtonFinkelstein.ipynb
• [ ] TOVEquation.ipynb
• [x] Geodesics.ipynb

[marcinofulus]

some minor changes proposes in https://github.com/marcinofulus/jupyter4edu/pull/48