Publish library ndt_unified_downloads

Full complement of new standard unified views  (#66)

Overhauled download views.
Cosmetic and bug fixes to upload views
Remove old ndt_unified_downloads (different location)
Hard coded to use production base_tables
Update units on MeanThroughputMbps and MinRTT
(Confirmed with A/B matching across the platform transition)
Remove three superfluous non-standard views
Indicate PREPUBLICATION status