Please improve the Dataflow error messages

[jaronc]

Please improve the error messaging when a Dataflow fails on setup. 

I spent over 3hr attempting to debug a Dataflow error with the only message being an "unexpected error" has occurred. After reviewing the network logs within Edge I noticed the far more helpful error, namely that I had a leading or trailing space in one of the entity headers. 

This was a 5min fix to 3hr due to a lack of actionable error messaging within the UI experience.  

[CharlesS]

I would add that the error messages should also be improved, not only on setup, but also in error logs for existing dataflows that fail or have warnings upon refresh.