Add 'article/edit' view

We will be able to simply edit an article on the frontend, but not update it yet.
Add 'ArticleController.edit' action

If routed here we will display the 'article/edit.jade' view
Add 'article/edit/:id' route

This will target ArticleController.edit with the article id and allow the user to edit the given article if it exists.
Add 'ArticleController.update' to attempt applying modifications to an article
Add '/article/update/:id' route for applying modifications to an article
Show links for 'showing' and 'editing' articles in the index

Adds 2 columns for that purpose
Add 'Edit' link in 'article/show' view
Merge branch 'updating_articles' into getting_up_and_running