We don’t want npmjs 5xx errors to cause config validation Issues in repositories.

Closes #1388

This PR updates Renovate to detect config validation problems and (1) stop processing, and (2) either raise an Issue if already onboarded, or (2) update the onboarding PR to reflect the error if still onboarding.

Closes #1300 

Repository logic code has been rearranged for better logic and file separation.

Closes #654