LPS-44472 Add references to Asset services in Layout service
LPS-44472 Handle Asset entities in Layout services
LPS-44472 Prevent conflicts when adding system events

If the system event exists, it is updated instead of trying to add a new one with the same id, which causes an Hibernate exception.
Revert "LPS-44472 Prevent conflicts when adding system events"
LPS-44472 Add deletion events properly and supress asset's automatic deletions event creation because for layouts we need a special logic what handles the private layout property
LPS-44472 Import assets
LPS-44472 Add categorization section to layout form
LPS-44472 Source formatting
LPS-44472 Fix broken test
LPS-44472 Regen