Moving approval notifications from EE to FOSS

app/mailers/emails/merge_requests.rb

app/services/merge_requests/approval_service.rb

app/services/merge_requests/remove_approval_service.rb

app/services/notification_service.rb

app/views/notify/approved_merge_request_email.html.haml

app/views/notify/approved_merge_request_email.text.haml

app/views/notify/unapproved_merge_request_email.html.haml

app/views/notify/unapproved_merge_request_email.text.haml

ee/app/mailers/ee/emails/merge_requests.rb

ee/app/services/ee/notification_service.rb

ee/spec/mailers/ee/emails/merge_requests_spec.rb

...c/services/merge_requests/remove_approval_service_spec.rb

spec/mailers/emails/merge_requests_spec.rb

spec/services/merge_requests/approval_service_spec.rb

spec/services/merge_requests/remove_approval_service_spec.rb

spec/services/notification_service_spec.rb