Add initial zh-CN translation based on ja.js dictionary strings

[boltomli]

Thanks for your interest in plotly.js!

Translations:

• Make a PR directly to the main repository
• Please @ mention a few other speakers of this language who can help review your translations.
• If you've omitted any keys from dist/translation_keys.txt - which means they will fall back on the US English text - just make a short comment about why in the PR description: the English text works fine in your language, or you would like someone else to help translating those, or whatever the reason.
• You should only update files in lib/locales/, not those in dist/

Features, Bug fixes, and others:

Developers are strongly encouraged to first make a PR to their own plotly.js fork and ask one of the maintainers to review the modifications there. Once the pull request is deemed satisfactory, the developer will be asked to make a pull request to the main plotly.js repo and may be asked to squash some commits before doing so.

Before opening a pull request, developer should:

• git rebase their local branch off the latest master,
• make sure to not git add the dist/ folder (the dist/ is updated only on version bumps),
• make sure to commit changes to the package-lock.json file (if any),
• write an overview of what the PR attempts to do,
• select the Allow edits from maintainers option (see this article for more details).

Note that it is forbidden to force push (i.e. git push -f) to remote branches associated with opened pull requests. Force pushes make it hard for maintainers to keep track of updates. Therefore, if required, please git merge master into your PR branch instead of git rebase master.

[etpinard]

Thanks very much for the PR, can you now please @ mention a few other speakers of this language who can help review your translations?

[etpinard]

Ping @boltomli - do you know any other Github users that are native speakers of zn-CN ?

[alexcjohnson]

Maybe @byronz could take a look?

[boltomli]

@Sunshow might have time to check as well?

[etpinard]

Ok - test-syntax is still failing, since I don't have push rights to @boltomli 's branch I'll go ahead and merge this PR and make a fixup PR in the next few minutes.