Tracking issue: Migration tool for versions > 0.6

[ohsayan]

With the disk format changing entirely in 0.7, and our commitment to backward compatibility, we will be releasing a migration tool for users to upgrade their datasets from 0.6. If someone is on 0.5, they will first need to upgrade to 0.6 and then to 0.7. For now, we will provide offline migrations, and we will explore live migrations in the (near) future.

// this tracking issue needs to be updated with tasks @glydr remind