Register decision to task

References:
* https://www.pivotaltracker.com/story/show/84436194

Notes:

Bug was *mostly* with the `register_decision_task` model which was independently performing an `update` on its paper.  This PR essentially works around this issue by setting the paper attributes and then calling save as a `before_save`.  This is not ideal, but fixing this is a much larger issue, so I opened up a separate pivotal card for the long term fix.  (https://www.pivotaltracker.com/story/show/84690814)

Also, we noticed another issue with saving upon losing focus, if the user immediately clicks the "Close" button.  I opened up a pivotal card here:  https://www.pivotaltracker.com/story/show/84700630


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AC + JN
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