Simplify users#index
Add fixtures for all models
Rename by_pinned scope of Topic to by_sticky
Update Paperclip, extract S3 bucket to env. var
Tidy up models, switch to Rails 3 style validators
Fix broken ApplicationHelper test
Add more unit tests for Topic and User
Remove unit tests of default Rails functionality
Move S3 config > config/environments/production.rb
Serve uploaded screenshots over https