Upgrade Ember and enable HTMLBars

Following the instructions from [here](http://reefpoints.dockyard.com/2014/11/30/htmlbars_calling_all_testers.html) I upgraded Ember to canary, added the ember-cli-htmlbars node package, and upgraded handlebars to 2.0.0. There are some warnings in the console, but everything seems to be working so far.