[WIP] The Events - Checkout Revolution

The aim of this PR is to get these checkout events under control.
Better separation of checkout process / order creation events.

  - [x] Add checkout events to security step
  - [ ] Add order creation related events to all checkout steps. These events deal with the order creation mechanism, independently of the checkout process. So they will be reused for backend order creation for example. We keep all the current checkout events for things related to the checkout process itself
  - [ ] ...