Cleaning and organization in cell/cell.py
Cleaning and organization in cell/shapes.py
Cleaning and organization in comm/pathloss.py
Ignore all files in the docs/Mathjax folder

Add "docs/Mathjax/*" to .gitignore.
Add the PathLossGeneral class

Make other classes such as PathLoss3GPP1 and PathLossFreeSpace inherit
from PathLossGeneral, which simplifies the code.