Show version and latest update date in download page

[mik-ohdsi]

Currently, there is a column "Latest Update" in the download page that actually shows the date stored in the "latest_update" column in the vocabulary_conversion table. However, this date represents the version of the source vocabulary, not when it was last updated by the vocab team. We propose to add an additional column for the version and use that information and fill the latest update column from the "latest_release_date" column in the vocabulary_release_stat table.

[mik-ohdsi]

this issue is also related to #164