Add versioning of builds to Jenkinsfile

[justaddcoffee]

To address #135 and also MS reviewers' request that we provide versioning for our builds

This PR:

• writes out all files for a build to a timestamped directory eg. 20201231 (including
  • merged graph in TSV format
  • an RDF version of the merged graph
  • the raw/ directory with the data ingested to make build
  • the transformed/ directory containing subgraphs
  • a stats directory with statistics about the build
  • the Jenkinsfile containing that actually ran the build
• copies this directory to a current/ directory so users can have a URL to retrieve the most current build
• also adds index.html files to each of the directories mentioned above, to allow browsing/listing of contents for directories

[justaddcoffee]

@kltm I think one remaining item that we need here is to update the Deploy blazegraph stage to point to the blazegraph jnl file here once we have run the master pipeline to completion