[37] Upgrade ActiveAdmin

Trello: https://trello.com/c/a3n3UqAN

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ActiveAdmin is two major versions behind.  Was working on something which requires 0.5 newer version so this seemed like a good time to perform the upgrade.

This upgrade ActiveAdmin from 0.4.4 to 0.6.0

The upgrade causes some styling problems with form submit buttons.  The simplest solution was to make the buttons conform to ActiveAdmin expectations, however this necessitated changing the javascript. Since I was editing the javascript, If fixed the currently broken behaviour associated with changing an articles status.

The process for different user classes works as follows.

> Writer starts working on an article.  By default it's a 'Draft'  The writer can either click "Update" to update their changes and save their draft, or "Ready to review" which means it's ready to be published. Once they click 'ready to review' they are unable to edit the article unless the editor makes it a draft once more by sending it back to them
> 
> When an editor logs in they now see a list of articles which are pending review on their dashboard.  They can choose any of these to review and do one of three things: Make some changes and save (update), Send it back to the writer for review (Send back for review) or Publish it. Sending it back to review marks it as a draft once more. 
> 
> When an editor is looking at a published article, they can either save some changes to it or (update) or unpublish it (unpublish).
> 
> In addition, editors can freely assign a writer to any article.
> 
> Writers are able to edit any draft article, including ones they are not the 'writer' for.