Ensure that JSHint is done after preprocessors.

JSHint will not attempt to read/process `*.coffee` files for example.

Would also be an issue when using sweet-js macros (as they may appear to
be invalid).
Merge pull request #1221 from rjackson/fix-hinting-for-coffeescript

Ensure that JSHint is done after preprocessors.
Allow addons to add blueprints.
Allow blueprints to export an object.

This allows blueprints from addons to have access to all of the internal
inherited functions from the EmberCLI `Blueprint` class without having
to have `ember-cli` as a dependency.

Also, make `addon.blueprintPaths` a function.
Refactor `ember update`.

* remove ad-hoc code
* create UpdateChecker model
* ensure all branches are possible
* don’t use rewire
Merge pull request #1195 from stefanpenner/begin-fixing-update-checker

Refactor `ember update` command.
Merge pull request #1222 from rjackson/blueprints

Allow Addons to provide blueprints.
Remove old update-checker utility file.
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