Add support for migrating briefs into new repositories

[FreshAlacrity]

example:

• for a project with
  • a brief in Google Drive
  • a Projects entry in the Navigator
  • a folder of associated assets and materials here in this repository
• first
  • export the brief and set it up as a readme doc with the usual sections
  • add project entry information to the repo
  • move any existing assets and materials into the repository
• then
  • remove the assets in this repository
  • rename the Google Doc to add '(ARCHIVE)'
  • update the project entry to reflect the new locations for files