adding support for CSRF Token to DS.RESTAdapter in store

Adding to DS.RESTAdapter the CSRF Token so that requests will work with Rails's protect_from_forgery. I have tested the generator on my machine. Here is a discussion that I had about how to support CSRF tokens:  http://discuss.emberjs.com/t/rails-cant-verify-csrf-token-authenticity-with-ember-data/4110/10