#715 Make MortalityEvents available to Blazer

[that-jill]

Checklist:

• I have performed a self-review of my own code,
• I have commented my code, particularly in hard-to-understand areas,
• I have made corresponding changes to the documentation,
• I have added tests that prove my fix is effective or that my feature works,
• New and existing unit tests pass locally with my changes ("bundle exec rake"),
• Title include "WIP" if work is in progress.

Resolves #715

Description

From the issue:

• Add organization_id column to mortality events
• Update code to scope mortality events to an organization
• Update the Blazer rake task to include Mortality Events
• Update tests accordingly
• Update seed data accordingly

Type of change

• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not
  work as expected)

How Has This Been Tested?

bundle exec rake

[that-jill]

Still WIP while I verify everything.