Folder content type fix for cleandata.sql,
Even if it's looks like issue with migration bundle - the sql data should be fixed and should looks the same as the data generated by the public API.

the main reason why it should be changed: after creating new content type using platform UI (without specifying the `description` in `Global properties`) the database field value for ezcontentclass/serialized_description_list will be `a:0:{}`, not `b:0;` - the purpose of this issue is to fix the differences. It also causing problems with migration bundle.

backstory: using kaliop/ezmigrationbundle (4.1.0)
and example migration with description update:

-
    type: content_type
    mode: update
    content_type_group: 1
    identifier: folder
    name: Folder
    description: 'A generic entity used to set up structures for storing content entities (articles, etc.).'
    name_pattern: <short_name|name>
    is_container: true
    default_sort_field: path
    default_sort_order: ASC

I was unable to run it, the error message:

  [Symfony\Component\Debug\Exception\FatalThrowableError]  
  Unsupported operand types   

trace:
 () at vendor/kaliop/ezmigrationbundle/Core/Executor/ContentTypeManager.php:725
 Kaliop\eZMigrationBundle\Core\Executor\ContentTypeManager->getMultilingualValue() at vendor/kaliop/ezmigrationbundle/Core/Executor/ContentTypeManager.php:170
 Kaliop\eZMigrationBundle\Core\Executor\ContentTypeManager->update() at vendor/kaliop/ezmigrationbundle/Core/Executor/RepositoryExecutor.php:85
...

steps to reproduce:
1. put the migration step into migration.yml
2. php app/console ezplatform:install clean
2.5 if the migration was used before, run: php app/console kaliop:migration:migration --delete migration.yml -n
3. php app/console kaliop:migration:migrate --path=migration.yml

Test list:

• install by ezplatform:install clean
• modify Folder content type (description, fields)
• create new Folder content
• check preview
• render the page with created content
• try to add subitem to created folder content
• add another langage to created content