Improve HTML Detection in History Support Middleware

Use built in ExpressJS methods for detecting HTML in the Accept header.
Merge pull request #1228 from jherdman/improve-html-detection-in-history-support

Improve HTML Detection in History Support Middleware
Remove extra test noise.

`runCommand` already prints the output, there is no reason to log it
again.
Merge pull request #1232 from rjackson/remove-extra-test-noise

Remove extra test noise.
Allow running tests in production.
Merge pull request #1230 from rjackson/use-environment-consistently

Allow testing of production assets.
Provide Ember CLI version to Project model.
Merge pull request #1239 from rjackson/provide-brocfile-with-ember-version

Provide Ember CLI version to Project model.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Provide Ember CLI version to Project model.
  Allow running tests in production.
  Remove extra test noise.
  Improve HTML Detection in History Support Middleware
Fix tree returned by addonTreesFor('styles') not being included
Merge branch 'styles-addon-trees'

* styles-addon-trees:
  Fix tree returned by addonTreesFor('styles') not being included