Resolve "Refactor backend"

Closes #160 (closed)

The entire backend refactored to:

sequenceDiagram
  participant Client
  participant Primary
  participant ProviderCanvas
  participant Canvas
  
  Client ->> Primary: /api/reviews
  
  Primary ->> ProviderCanvas: /api/courses
  ProviderCanvas ->> Canvas: /api/v3/courses
  Canvas -->> ProviderCanvas: Courses info
  ProviderCanvas -->> Primary: Generalized course info
  
  loop Every Course
	  Primary ->> ProviderCanvas: /api/course/{course}/reviews
	  ProviderCanvas ->> Canvas: /api/v3/courses/{course}/assignments
	  Canvas -->> ProviderCanvas: Course assignments info
	  ProviderCanvas -->> Primary: Generalized review info
  end
  
  Primary -->> Client: Collected reviews

View #160 (closed) for more information.