Fix date issues on editions

* Removed first_published_at on speeches as it should not be there
* Converted dates to datetimes
* Added in a js warning notification if you try and set something for the future


Relates pivotal tickets:
https://www.pivotaltracker.com/story/show/48147091
https://www.pivotaltracker.com/story/show/48077405
https://www.pivotaltracker.com/story/show/45325579