Make Description and Authors 'required' on the edit package metadata page.
Fixes #1468 - Add the 4000 char string length limit on description which actually exists in the gallery, so people get validation errors instead of seeing their edit succeed.
Remove the cluttersome required labels.
Merge branch 'tilovell-1468-descriptionAndAuthorsShouldBeRequired' into qa

Conflicts:
	src/NuGetGallery/RequestModels/EditPackageVersionRequest.cs