Now the Worker and the Manager share the same database initialisation
code (enabling foreign key constraints + write-ahead logging).
The foreign key constraints were already enabled before, but now it's done
with (a copy of) the same code as the Manager.
Change the package base name of the Go code, from
`git.blender.org/flamenco` to `projects.blender.org/studio/flamenco`.
The old location, `git.blender.org`, has no longer been use since the
[migration to Gitea][1]. The new package names now reflect the actual
location where Flamenco is hosted.
[1]: https://code.blender.org/2023/02/new-blender-development-infrastructure/
Convert the database interface from the stdlib `database/sql` package to
the GORM object relational mapper.
GORM is also used by the Manager, and thus with this change both Worker
and Manager have a uniform way of accessing their databases.
