Ensure files are served through Broccoli middleware
Split computed macros into a separate module
Split dependent key management into separate module
[BUGFIX beta] Use injected test helpers instead of local functions.

Since we are injecting the application with our helpers (into the
`App.testHelpers` hash), we should be using that helper and not simply
calling the function in local scope.

As the tests show, this allows a user to override the internal helpers
with a taylored version for their scenarios.
[BUGFIX beta] Add alias descriptor
[BUGFIX beta] Regression test for #5112