User Dashboard: Bookmarks

[BrianZanti]

Background: Ability to bookmark is already built out. This story should display things that are already bookmarked. Bookmarking occurs in UserVideosController#create if you want to explore the model relationships.

As a logged in user
When I visit '/dashboard'
Then I should see a list of all bookmarked segments under the Bookmarked Segments section
And they should be organized by which tutorial they are a part of
And the videos should be ordered by their position

• Only makes one query to the database (no n+1 queries)
• Avoids loading all videos into memory