Add Exit Codes

[tay1orjones]

Hi, I'm interested in adding a step to my Travis CI production deployment process that verifies that we have all translations needed and no conflicting IDs. If there are issues, the deployment should be halted.

This currently isn't possible, as manageTranslations always exits with success code 0. If there are conflicting IDs or untranslated keys, it still exits with a success code 0. Ideally, this would return 1 in those cases. With proper exit codes, CI tooling would be able to catch these issues upstream before a production deployment.

I think it would be beneficial for this to be the default behavior, although it could also be set behind a flag of some sort. Thoughts?

[GertjanReynaert]

Interesting idea, mind giving it a try in a pr?