fetch: Allow secondary_resource to be optional and still define params
Restructure project with models/ dir, flat namespace
Extract Badge class into its own file, remove references to StackExchange module
Refactor StackOverflowService to be an instance instead of static
Rename StackOverflowService to StackExchangeService
Add StackExchangeService#site, default to stackoverflow
Add StackExchangeService#api_version param
Rename unearned_badge_job_spec.rb to unearned_badges_spec.rb
unearned_badges: refactor to fetch user badges with service.fetch