Implement pipeline hooks, extracted from !5525

CHANGELOG

app/controllers/concerns/service_params.rb

app/controllers/projects/hooks_controller.rb

app/models/ci/pipeline.rb

app/models/hooks/project_hook.rb

app/models/hooks/web_hook.rb

app/models/service.rb

app/services/ci/create_pipeline_service.rb

app/views/projects/hooks/_project_hook.html.haml

app/views/shared/web_hooks/_form.html.haml

...igrate/20160728081025_add_pipeline_events_to_web_hooks.rb

db/migrate/20160728103734_add_pipeline_events_to_services.rb

lib/api/entities.rb

lib/api/project_hooks.rb

lib/gitlab/data_builder/pipeline_data_builder.rb

spec/lib/gitlab/data_builder/pipeline_data_builder_spec.rb

spec/models/build_spec.rb

spec/models/ci/pipeline_spec.rb

spec/requests/api/project_hooks_spec.rb