Contact sponsors via email

[wolframkriesing]

We want all sponsor items to be covered and need to contact sponsors therefore. In the past years we wrote emails to previous sponsors. Going through the past issues might reveal a lot of them who are still interested ... or find new ways to find sponsors

see #570 for 2019 sponsors

[Narigo]

Don't forget to tell potential sponsors that they may post jobs at JSCC (see https://github.com/jscraftcamp/website/issues/788)