[Scenario] Database migration script

Add database migration script corresponding to
code changes pulled in nasa/MCT-Plugins#146.

Specifically:

* Clear out tag associations from repository
  components (these are no longer bootstraps,
  having been moved deeper into the taxonomy.)

* Change base display names of individual
  repositories to match naming specified in
  nasa/MCT-Plugins#134. So, User Tags
  becomes My Tags instead.