Rename all d6_i18n migrations

The d6_i18n_some_migration.yml migrations are renamed to d6_some_migration_translation.yml. This is to comply with the convention that migrations for translations end with '_translation.yml'.

Migrations

• Any reference to d6_i18n_system_site.yml was renamed d6_system_site_translation.yml
• Any reference to d6_i18n_user_settings.yml was renamed d6_user_settings_translation.yml
• Any reference to d6_i18n_user_mail.yml was renamed d6_user_mail_translation.yml
• Any reference to d6_i18n_user_profile_field_instance.yml was renamed d6_user_profile_translation.yml
• Any reference to d6_i18n_system_maintenance.yml was renamed d6_system_maintenance_translation.yml

Source plugins
If you extend from the following classes, you'll need to update your code to reference the new Translation classes.

• Any reference to I18nProfileField.php now references ProfileFieldTranslation.php
• Any reference to i18nVariable.php now references VariableTranslationTest.php