Validation: relate validation errors to editors

[dasch124]

h1. Description

As usual, the various levels of validation only report errors for file names + line numbers.
To ease managing the resolution of errors in the feature documents, each error should be assigned to the editor of the respective feature value observation element the error was caused.

[dasch124]

implemented in the validation notebook which now returns the line of the error and tries to map it to the offending fvo.