Data model migrations #8
Description
Once the initial climate data model and software layer are relatively stable we should include migration files with the physical data model that records how the data model changes over time (using alembic).
This will allow the software to keep track of which version of the database schema the code works with and also automate upgrades and rollbacks.
This is potentially the final issue to conclude https://github.com/opencdms/pyopencdms/issues/73