Testem cleanup

From Bill's PR #16:

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* Renamed testem.yml to testem.json as the content is JSON
* Renamed test files *.js.coffee to *.coffee since compiling replaces .coffee ext. with .js
* Changed order of loading scripts in the testem.json, settings needs to load prior to Ember.js 
* Changed the way Ember is set to test mode so that it can be set to test prior to loading Ember.js
* Moved out code `Ember.Router.reopen({location: 'none'})` out of settings since it's loaded prior to Ember.js; added as in a `beforeEach` fn on the ember_in_test_spec.coffee spec.

Passing tests:

* Chrome 2/2
* PhantomJS 2/2/
* Safari 1/2
* Firefox 1/2

Safari and Firefox complain about Ember.js in test mode:

    Error: assertion failed: You have turned on testing mode, which disabled the run-loop's autorun. You will need to wrap any code with asynchronous side-effects in an Ember.run (http://localhost:7357/js/libs/ember.js:52)

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I fixed a few details; otherwise this is his.  I closed his PR #16 w/o merging since this replaces it.