Separate `translation-tools` repo where to put tools that can be shared by different translation projects

[josix]

Probably out of the scope of this PR, but eventually I think it might be useful to have a separate translation-tools repo where to put tools that can be shared by different translation projects.
If the tools are in a separate repo, it is also not necessary to create a hidden dir that is not easily discoverable (using _scripts might be a better option, unless it interferes with something).

Originally posted by @ezio-melotti in #378 (review)

[ezio-melotti]

cc @JulienPalard

[JulienPalard]

Something like https://github.com/afpy/poutils?

[josix]

I guess we could create po-google-translate as another utility tool repo and add it to poutils.

[JulienPalard]

Addition to poutils are welcome, that just a "meta-package" (it has no content, only dependencies).