Ignore encrypted attributes in Import/Export

• Regenerates tokens for all models that have them
• Remove variables, since they are basically just storing encrypted data
• Bumped version up to 0.1.6

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/24458

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• Changelog entry added
• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together