[#47] Initial integration with Papertrail - Articles now have versions

* Article#versions for an array of ArticleVersion objects
* ArticleVersion table for just the article versions

Conflicts:
	app/models/article.rb
	db/schema.rb
[#47] Ignore #access_count when detecting for changes to Article.

We dont' want to create new versions every time the article is accessed.
[#47] Adds Article#status to ArticleVersion

This lets you pick versions depending on their status.

Conflicts:
	db/schema.rb