Release branch 0.70.0

[Tim]

Hi everyone,

I've created the branch for our upcoming release: 
https://github.com/apache/incubator-streampipes/tree/rel/0.70.0

Please feel free to test it.
If there are any bug fixes that need to be included in the release, you 
can add them directly to the release branch.
If we don't have any major issues, I plan to proceed with the release in 
the next week or two.

Best
Tim