Add default predicates implementation on Triage::Event

Why

Combat issues like:

• #115 (closed)

What

Add default predicates implementation on Triage::Event

The default implementation will always just return false.

The rationale behind this is that we're seeing too many errors that we're assuming a specific event while it is not. When this happened, we're usually using a predicate method so perhaps it makes sense to provide a default implementation which just returns false.

Action items

• When adding a new Triager, verify that it has been added to the DEFAULT_TRIAGERS in triage/triage/handler.rb in the appropriate order.
• If applicable, identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Week-in-review