Implement ability to perform cascade operation on event

[sleshchenko]

It's needed to have ability to modify(create|remove|update) some objects on another object modification. So modifications should be made in one transaction to be sure that everything is modificated or nothing. If cascade operation is failed then transaction must be roll backed and original exception must be thown. For example, on user removing we should remove all his workspaces. If it's not allowed to remove workspace then REST API Client should get original exception like -> 409 "Running workspace can't be removed"