Update rules for Rails 4

Rails 4 moves tests from test/unit/MODEL_test.rb to test/models/MODEL_test.rb
Update the rules to run the tests in either location.
Allow for nested tests, so these run when app/models/widget.rb changes:
- test/models/widget_test.rb
- test/models/widget/associations_test.rb
- test/models/widget/assembly_test.rb

Update test locations for controller and helpers as well.