This commit sets `tap_failed_tests_only` to `true` in our testem config, so now only the failing tests will show in our GitHub CI Ember test runs, which saves developers from having to hunt through all of the passing tests using GitHub's janky console output scrollback.
* DEV: Use custom tags rather than handlebars server side
These will be skipped if they are ever rendered in a document. The
handlebars really messes stuff up.
* DEV: Build our own locale file for testing purposes
We can't practically proxy everything in test mode, but we can
approximate the logic and build our own locale file for testing purposes
that works quite well. This allows us to run tests without a proxy.
* DEV: Support for testem runner for ember cli tests
