[L1-1] Revise Python script and adapt Notebook

CSS style file:
* Add script to reset equation numbers.

Python script for phugoid:
* Revise script and complete code comments and docstrings.

Jupyter Notebook 01-1:
* Cast all equations between '$$' signs.
* Correct small typo.
* Display correctly SVG figure.
* Update link to documentation for magic functions.

Author: mesnardo