Generic update between major versions

[vincent-herlemont]

If there are breaking changes between major versions of the database, a manual solution is currently implemented for each change, see the features upgrade_0_5_x and upgrade_0_7_x (available for example in v0.8.0).

It would be useful to find a generic way to handle this, allowing users to manage these issues themselves easily. Proposal:

• Enable multiple versions of the Native DB to coexist (currently impossible)
• Create a simple transfer function db_v1.upgrade(db_v2).

TODO

• Investigate