[Validation] Add 'emails' validation for comma separated

[witold-markowski-sentaca]

The email validation passes when entered multiple email addresses in the form, like:

a@bc.de , f@gh.ij

Emails doesn't have to be "comma separated" in the example; you can enter multiple characters between emails and it will be still validated as a valid email address.
You can use @paulborza's JSfiddle from #3755 issue to test it.

Shouldn't it allow to enter only one valid email address?

[jlukic]

I think it makes sense to add another validation type emails for comma separated lists

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 30 days if no further activity occurs. Thank you for your contributions.

[brunotourinho]

this would be a nice implementation. Any workaround? I'm interested in file types validation as well.