Rename reply_by_email to incoming_email to prepare for the future.

app/mailers/notify.rb

app/models/sent_notification.rb

app/views/admin/dashboard/index.html.haml

app/workers/email_receiver_worker.rb

config/gitlab.yml.example

config/initializers/1_settings.rb

doc/README.md

doc/incoming_email/README.md

doc/incoming_email/postfix.md

lib/gitlab/email/receiver.rb

lib/gitlab/incoming_email.rb

lib/tasks/gitlab/check.rake

spec/lib/gitlab/email/receiver_spec.rb

spec/lib/gitlab/incoming_email_spec.rb

spec/support/stub_configuration.rb

spec/workers/email_receiver_worker_spec.rb