Skip image errors on create from published edition

content that was imported had smaller inline
images than the ones we allow - 960x640. for
now, we are allowing such images to be carried
over to new drafts created from such published
editions. there will be more work done on this
as part of:

https://www.pivotaltracker.com/story/show/69931140
Merge pull request #1439 from alphagov/skip-image-validation-when-creating-from-draft

Skip image errors on create from published edition