Fix missing tests in event_spec.rb

* Add a spec for validates :uuid, presence: true (didn't exist)
* Add tests for attr_accessibles in their own block
* Add class name to should belong_to(:owner) to be more specific

Cleanup:
* Remove unused DelayedJobSpecHelper
* Don't create a variable if only used once - make direct ref
* Shorten matching message for name validation

Formatting:
* Use Newlines to group associations which are similar
* Create separate spec group for associations, validations
* More granular association blocks for each subgroup
* Move add_errors_if_no_suggestions validation to separate block in event.rb
* Add spec for add_errors... to it's own block
* Add separate before_validation spec block
* Group after_create callbacks into a single spec block

Trello: https://trello.com/c/EHrIO1Ee