Plugin Directory: Clarify language for submission errors

[Ipstenu]

The attached patch standardizes all the errors with an 'error' to describe what the problem is, and then a longer explanation of what to do to fix it.

It also fixes directions on if you try to resubmit the same plugin twice.

[Ipstenu]

Updated patch with directions on accepted submission because people aren't reading.

[Ipstenu]

This one has clearer notes about whitelisting us (not in the email) so people know who to expect the email from *SIGH*

[ocean90]

The email should be a placeholder in the strings so it doesn't get translated. Don't forget to update the translator comments.

[tellyworth]

In 5471:

Plugin directory: clarify error messages during submission process. Props @ipstenu.

Fixes #2788

[ocean90]

Thanks for ignoring my comment...

[SergeyBiryukov]

2788.4.diff​ switches the email address to a placeholder and updates translator comments, as per comment:2.

Moving to v3.0, as the ticket already has a commit that just needs a follow-up.

[SergeyBiryukov]

2788.5.diff​ is a combined patch with the changes from #2830, as they have some overlap. Whichever one gets committed first, should fix the other one as well :)

[SergeyBiryukov]

2788.6.diff​ is the same as 2788.5.diff​, but with raw email address converted to a mailto: link for better UX.

[tellyworth]

Can someone confirm whether was fixed with r5561, or if there are further changes needed.

[SergeyBiryukov]

[5561] includes the fix for the issues raised in comment:2.