Search functionality and Test fix

[eidun10]

• Placed table of articles in a partial. This is because we want to use the same in the search view(article/search.html.erb). Also added toggle to sort the table in ascending/descending order
• Replaced template dropdown in navbar with search bar. The logic of the search works to perform a case-insensitive search on both title and content fields of our Articles
  Note: app/views/articles/search.html.erb is currently the same as app/views/articles/search.html.erb, but this could change in the future

Other:

• Added input field for Author when creating an article
• Modified test/controllers/articles_controller_test.rb to not use fixtures files but create article(s) variable within its test scope. It helps so it does not affect the model tests