Extract data import steps to a helper to allow reuse
Import now has direct access to the editions it imported
Add force-publish button to import index

Only when the import is a success, and only have it enabled when the import is force publishable (this behaviour might change).  It is force-publishable when:

a) it has succeeded
b) it actually created some imported editions
c) none of those are in the 'imported' state
d) some of them are in the 'draft' state

NOTE: the force_publish route doesn't go anywhere yet
Provide ImportsController#force_publish

It calls through to Import#force_publish! which at the moment is a no-op.  More to come.
Provide ForcePublicationAttempt to record Import#force_publish! results

It's based heavily on the Job / ProgressLogger stuff in Import itself, but it:
* doesn't need a separate connection (failure to force publish one document shouldn't stop the whole process)
* just records everything in a text log rather than storing objects you can interrogate (like ImportError)
* doesn't record the current document it is working on (so you won't be getting on the go feedback)
Provide a view for an imports most recent force publication attempt

Heavily based on what the existing view for showing an import.  Also provide some detail about *why* the user can't force publish the import.
Feature to describe force publishing process
<pre> tags can't live inside <p> tags.
Merge pull request #173 from alphagov/force-publish-an-import

Force publish an import