sankey separators

[simonerubiu]

Referring to #2859 I find out a solution to solve this issue with sankey separators.
While fixing this issue I find out that the separatethousands options there isn't in sankeycharts, and I try to implement it in the correct way. Another problem I found is that the numSeparate function not works properly with 4length numbers,

[etpinard]

Thanks very much for your help @simonerubiu !

So, if I understand correctly this PR does 4 things:

1. fixes the italian translation
2. fixes layout.separators for sankey traces (as tracked by Sankey separator #2859)
3. adds separatethousands to sankey traces
4. fixes a bug with Lib.numSeparate

which is a little much for one PR. Moreover, we wouldn't want to pollute our commit history with those ".gitingore" -> "revert .gitignore" commits off this branch.

So, I suggest:

• making 1 PR just for item 1,
• create a reproducible example for the Lib.numSeparate bug you discovered so that we can confirm it's in fact a bug
• make a separate PR for items 2 and 3 and make sure all the tests pass

Note also, you changed the file mode in the files you modified from 100644 → 100755. Please try to avoid that.

Thanks again for contributing to plotly.js. Let me know if you have any other questions.

[etpinard]

I'll close due to lack of activity.

@simonerubiu feel free to open another PR (or PRs) following my recommandations in #2894 (comment)

Thanks again for contributing to plotly.js!