snippet locale copy command

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | none
| Doc           | none
Just updated at less as possible to get the command working, that's why I don't change more here.

And I am still not convinced by the `ContentMapperRequest`... Today I also found out why, it's a halfway implementation of the command pattern. I already had the idea to implement the command pattern for the `ContentMapper` in general, would also make this class a lot less complex.

I also add this comment to the issue I have created.