Specify additional headers for RESTAdapter.
Declared ajaxHeaders.
Start consolidating API around records

Thus begins the elimination of lazy materialization
Make find and findAll tests pass

I staged all of the existing tests in ember-data/old-tests and will move
them over one at a time to get them passing.

The highest priority right now is to get all tests passing again.
Eliminate lazy materialization from belongsTo

Note that I have punted embedded belongsTo for now, but it should be
pretty straight forward to add to the serializer once hasMany is done.
fetchRecord replaced findById here

This was an error in the previous commit
Allowing inverse relationships to be nullable.

Now we can prevent `DS.Model.inverseFor` from automatically looking for
a relationship and identifying the wrong relationship in some cases
First hasMany tests passing
Eagerly generate the jQuery expando on window

In tests, this will make the QUnit global checker run clean
Add puma to the Gemfile

Puma is much faster than Webrick
Client ID generation passing
Lifecycle Hooks test passes
Reloading records test now passes

Also removed some remnants of lazy materialization
Save test is now passing
Moved reload_test into integration/records
Got record persistence tests passing
Get model tests passing + add transforms
Get adapter tests passing

Removed adapter configuration of mapping and transforms as this will
become a serializer responsibility
Debug test is passing
Fixture tests are passing