[META] Port all events to 8.x

To get started:

• pick your event from below, create an issue for it and edit the list to reference the issue
• look at the docs how to write events: http://thefubhy.gitbooks.io/rules/content/extending_rules/events.html

Issue list:
based on D7 modules/events.inc

• Entity (derivative plugins based on entity_type replace Node, Comment, Taxonomy & User-specific events from below)
  • entity_delete - After deleting an entity_type #2538646: Port "After deleting an entity_type" event to D8
  • entity_insert - After saving a new entity_type #2538694: Port "After saving a new entity_type" event to D8
  • entity_update - After updating an existing entity_type #2539006: Port "After updating an existing entity_type" event to D8
  • entity_presave - Before saving an entity_type #2513480: Port "Before saving entity" event to D8
  • entity_view - entity_type is viewed #2539112: Port "entity_type is viewed" event to D8
• System
  • cron - Cron maintenance tasks are performed #2624846: Port "System : Cron maintenance tasks are performed" event to D8
  • init - Drupal is initializing #2539700: Port "init" system event to D8
  • watchdog - System log entry is created #2624848: Port "System:watchdog:system log entry is created" to D8
• Node (see Entity above)
• Comment (see Entity above)
• Taxonomy (see Entity above)
• User
  • Other ones (see Entity above)
  • user_login - User has logged in (done)
  • user_logout - User has logged out #2548345: Port User has logged out (user_logout) event to D8