[WIP] Category job

| Q                    | A
| -------------------- | ---
| Bug fix?             | N
| New feature?         | Y
| Behat pass?          | ~
| Tests pass?          | ~
| Checkstyle issues?   | ~
| PMD issues?          | ~
| Changelog updated?   | ~
| DB schema updated?   |
| Migration script?    |
| Doc PR               |
Rename as CategoryToStructuredArrayNormalizer