Introduce a new configuration field to set the DateTime Format at least for the import/export

[ulftietze]

This pull request is one step of the general problem, that the import/export is facing, when it's come from export to reimport the same file. One related issue is the #61. This PR fixes one of the reasons, that this could not work.

We ran here into the problem, that the dateformat in standart format looks like eg. German: 12.11.18 15:42:45 US: 11/12/18 15:42:45

We can't reimport this, because of the PHP "strtotime()" function. If you called this function with this dateformat, we ran into the issue, that this date could not resolve the "18" as year at the end. Probably PHP tried to lookup for the exact year, and this could be 1918, 2018, 2118, and so on. So this breaks everything.

Now you can set your default datetime in Stores > Configuration > General > Locale > DateTime Format. It's saved under 'general/locale/locale_date_format'.

Fixed Issues (if relevant)

1. Probably a small thing of #61

Contribution checklist

• [x] Pull request has a meaningful description of its purpose
• [x] All commits are accompanied by meaningful commit messages
• [x] All new or changed code is covered with unit/integration tests (if applicable)
• [ ] All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

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[dmanners]

@ulftietze I think your git user and github user are not the same or linked. Could you please check that and get back to me on this.

[dmanners]

Hi @ulftietze I am going to close this PR due to inactivity. If you have time and want to come back to this PR please feel free to address the issues raised in the review and reopen this PR.

Thanks