PIM-2045 Normalize import/export translation keys

| Q                   | A
| ------------------- | ---
| Bug fix?            | yes
| New feature?        | no
| BC breaks?          | yes
| Tests pass?         | yes
| Scenarios pass?     | ? build 691
| Checkstyle issues?  | no
| Changelog updated?  | no
| Fixed tickets       | PIM-2045
| Doc PR              | https://github.com/akeneo/pim-docs/pull/16