WIP - started refactoring cycle analytics median stuff into stages

app/models/cycle_analytics.rb

lib/gitlab/cycle_analytics/base_event.rb

lib/gitlab/cycle_analytics/base_stage.rb

lib/gitlab/cycle_analytics/code_event.rb

lib/gitlab/cycle_analytics/code_stage.rb

lib/gitlab/cycle_analytics/events_query.rb

lib/gitlab/cycle_analytics/issue_event.rb

lib/gitlab/cycle_analytics/issue_stage.rb

lib/gitlab/cycle_analytics/metrics_fetcher.rb

lib/gitlab/cycle_analytics/plan_event.rb

lib/gitlab/cycle_analytics/plan_stage.rb

lib/gitlab/cycle_analytics/production_event.rb

lib/gitlab/cycle_analytics/production_stage.rb

lib/gitlab/cycle_analytics/review_event.rb

lib/gitlab/cycle_analytics/review_stage.rb

lib/gitlab/cycle_analytics/staging_event.rb

lib/gitlab/cycle_analytics/staging_stage.rb

lib/gitlab/cycle_analytics/test_event.rb

lib/gitlab/cycle_analytics/test_stage.rb