This moves `TemplateAssertions` out of the `test_case.rb` file and into
it's own `template_assertions` file. It still inherits from
`ActionController`.`
This is in preparation for combining the code for Integration tests and
Controller tests. This will need to be it's own file to be added to the
`requires` for Integration tests. This does not currently change ANY
behavior, just moving it for access later on.
