Add functionality that you can lint your translation files (feature)

[buchtadan]

This pull request adds a new feature that allows user to configure wether they want to create a translation file(s) or check if the given translation file(s) has already all the necessary translation-key's in it.

The intension behind this feature was, that you can integrate a 'translate-extract-check' to an ci pipeline or so.
Not sure if you want to add it in this repro or if you see it more in an other package, something like ngx-translate-linter or so.

It helped us in our project, but we had to create an extra fork, merge this functionality, publish it and so. So I would love to see this feature, not only because it would help us but more towards that I think it's a good addition.

Keep up the great work.
Let me know what you think and greetings.