Aggregate all details of a validation run in a single downloadable file

[ddhar28]

As a user, one should be able to download a single file containing all details of that validation run (stats, errors, warnings and affected external-ids) from the Validator result page.

Acceptance criteria

• [x] Downloadable link in Validator result page

• [ ] File name must contain validation run timestamp

• [ ] File must have the following content:

• Stats: Number of total stories, failed and valid stories and other information if any

• List of all errors and warnings if any with corresponding affected external-ids

[radhika-c]

1. Given input to validator, results page should have only single downloadable link.
2. Name of the file should be appended with time-stamp.
3. file should have following fields(error-type,path,log-level,external-id).

[RashmiMelagiri]

Tested but still production deploy is pending.