[Marketing] OSGeo Events updated

[Astrid Emde (OSGeo)]

Hello all,

I updated the OSGeo events page and marked some of the events as 
canceled.

https://www.osgeo.org/events/

I also added the upcoming online events.

@Enock - is it ok, if you add the SOTM 2020 as event. 
https://2020.stateofthemap.org/

Then we could tweet and ask our community whether there are more 
(online) events to come. Would be great to do this before or right after 
FOSS4GUK 17.6.

Astrid