Fix the database migration that adds `NOT NULL` clauses. It used
`INSERT INTO temp_x SELECT * from x;`, and the `*` returns the fields in
the order they are defined on the table. Since this might be different from
the order that the `INSERT INTO temp_x` expects, strange problems can
happen where columns get swapped (or constraints can fail on columns that
they should not fail for, because they got fed data from a different
column).
Replace GORM's auto-migration with Goose. The latter uses hand-written
SQL queries to apply database schema changes, which is safer and easier to
understand than what GORM is doing.
