Add Lumi

[intelliant01]

https://lumi.education/
https://github.com/lumieducation/lumi

[intelliant01]

Integrated. Requires internet at least for the first time or whenever a content type needs to be fetched. Need to figure out a way similar to Gcompris to keep at least one copy of each of the content types offline.

[intelliant01]

Was not working for RPi. Fixed with Lumieducation/Lumi#2290 (comment).