Downloaded IGRF data and cleaned it on notebook

I had to interpolate some nan values in the data and make a 180x360 grid
with it. Saved all quantities to a single csv file.

Will delete the cleaning code from the notebook to make it cleaner for
the students.
Change is too small, need every decade

Need to download all the data from the last century and show every
decade.
Calculate IGRF using Geomag 7

Was able to calculate for the last century and save to a CSV.
The notebook contains instructions for calculating.  I'll delete the
code for that later to clean up the lesson.
Browse IGRF over time, mag and anomaly of a cube
Add instruction to practice 1 mag

Had to remove the translations part of the article template because it
was thinking that pratica1 grav is a  variant of pratica1 mag.
Merge branch 'mag-pratica1'