Tweaks to gitignore

* adds `_site` and `_posts` to avoid shenanigans when switching from
  `gh-pages` branch
Add ES6 Import Validation

- Add dependency broccoli-es6-import-validate
- Add validateJs tree (only when env !== 'production')
Merge pull request #285 from twokul/gitignore

Tweaks to gitignore
[fixes #302] although location auto requires server side support, I would like to push for it as the default and aim to provide the appropriate server side components to make it seamless.
document.location.origin is not needed, and fails in IE
Merge pull request #209 from jgable/es6ImportValidate

Add ES6 Import Validation
Improve CSS preprocessors situation
Merge pull request #317 from HeroicEric/fix-css-preprocessors

Improve CSS preprocessors situation
Update README.md
[Fixes #324]
Merge pull request #325 from HeroicEric/fix-plain-css

[Fixes #324]
remove blueprint to prevent confusing for now, we can re-add it once we have time to make it work.
Version bump and updated CHANGELOG
Merge pull request #329 from twokul/version-bump-23

Version bump and updated CHANGELOG
Introduces broccoli-bower
Merge pull request #333 from twokul/broccoli-bower

Introduces broccoli-bower
Update CHANGELOG.md

Fix typo.
Merge pull request #336 from jbrown/patch-1

Update CHANGELOG.md
use load-initializer vendor'd package

see https://github.com/stefanpenner/ember-app-kit/pull/588
Merge pull request #337 from ghedamat/mattia/test-initializers

use ember/load-initializer vendor'd package