Week 5 - Checkpoint: Destroy
+ Hulk smash CRUD!
+ Added destroy method to Topics controller
+ Added destroy button to Topic view
+ Updated Topic model to cascade delete dependents
+ Added authorization to Topic controller destroy method
+ Wrapped view so destroy button is only shown to authorized users.
+ Added destroy method to Posts controller
+ Added destroy button to Post view
+ Updated Post model to cascade delete dependent comments
+ Wrapped view so destroy button is only shown to authorized users.
+ Added destroy method to Comments controller
+ Added delet button to posts
+ Made delete button render only for authorized users.