ZIM Kids has been converted to const, let and arrow functions

[abstract]

ZIM Kids at https://kids.zimjs.org has been converted from var and anonymous functions to const, let and arrow functions. Thanks to all those who offered their recommendations. The updates take place in the following files:

https://zimjs.org/magic
https://zimjs.org/slate

and the code and info pages for the three levels for the 8 basics tutorials, 4 bugs tutorials and 4 things tutorials - in other words 2x3x16 = 96 pages.

[karelrosseel82]

@abstract can you also update all stage.update() to S.update()

[abstract]

Okay - those should be updated now to S.update().