Integration test for importing official docs
Get rid of unnecessary hoop jumping.

I'm not exactly sure what having this separate object for setting the
meta attributes on an attachment was giving us so I'm ripping it out.
Add parlimentary paper info support to importer.
Don't force import columns unnecessarily

We don't actually require a policy or document series to validate new
documents, so there is little point requiring their presence in the
importer. If anything, it's an inconvenience to have to include empty
columns.
Merge pull request #718 from alphagov/hoc-command-imports

Update importer to support new official document attachments

https://www.pivotaltracker.com/story/show/49849655