We need some systematic way to do migrations #662
Description
There have been changes to the database schema in the past, and of course there is the big change between (current) stable and next, and there is no systematic, let alone automatic way to distribute and/or apply these changes to existing applications.
We need that.
We should probably look into something like flyway or liquibase, but even a scripts/sql folder like Opencast has would be preferable to nothing. The latter is a pain to make work across platforms, though. Plus, it still has the issue of “discoverability.” For that to work properly, we would probably have to go back to “proper” releases. See also #661.