Convert class activites to RST and tranlaste them to German

[fmaussion]

We recently added two class activities to a US based platform:

• https://serc.carleton.edu/teachearth/activities/250452.html
• https://serc.carleton.edu/teachearth/activities/250446.html

These activities should be readily applicable to a german high school class. I suggest to create a new rst file in this folder: https://github.com/OGGM/oggm-edu/tree/master/docs/activity_sheets that we will link to from the main page.

For example:

• oggm_edu_lab_1_de.rst for a german translation of lab 1
• oggm_edu_lab_2_de.rst for a german translation of lab 2

The links to teaching materials on the SERC platform have to be replaced by german translations as well, but this can be done in a second step.