[meta] standards cleanup to get ready for getting into core

Problem/Motivation

Since we want to get config translation into core, we need to make sure it meets the core gates. To make the chunks manageable, one issue per file.

Proposed resolution

Per core-gates standards, please add docs and standards fixes for each of the below issues. References to the standards:
https://drupal.org/core-gates#documentation
https://drupal.org/core-gates#documentation-block-requirements

Remaining tasks

review issues
work on those that need work

#2038743: docs cleanup use configuration instead of config
#2028127: clean up property names to be camel case instead of underscore separated words to cleanup to get ready for getting into core

./config_translation.admin.css #2011294: config_translation.admin.css standards cleanup to get ready for getting into core
./config_translation.api.php #2011320: config_translation.api.php hooks standards cleanup to get ready for getting into core
./config_translation.info.yml - Looks OK.
./config_translation.module #2011348: config_translation.module standards cleanup to get ready for getting into core
./config_translation.services.yml #2017887: config_translation.services.yml standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/Access/ConfigNameCheck.php #2017969: ConfigNameCheck.php standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/ConfigEntityMapper.php #2017975: ConfigEntityMapper.php standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/ConfigGroupMapper.php #2017977: ConfigGroupMapper.php standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/ConfigMapperInterface.php #2017979: ConfigMapperInterface.php standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/Controller/ConfigTranslationController.php #2017981: ConfigTranslationController.php standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/Form/ConfigTranslationDeleteForm.php #2017983: ConfigTranslationDeleteForm.php standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/Form/ConfigTranslationManageForm.php #2017985: ConfigTranslationManageForm.php standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/Routing/RouteSubscriber.php #2017987: RouteSubscriber.php standards cleanup to get ready for getting into core
./lib/Drupal/config_translation/Tests/ConfigTranslationUITest.php #2017989: ConfigTranslationUITest.php standards cleanup to get ready for getting into core

User interface changes

No.

API changes

No.