EmberCLI Rails Addon

This is an integration piece between ember-cli-rails (the rubygem) and the EmberCLI applications they reference. This addon is responsible for the following

• Setting expected build variables without the user having to manipulate their EmberCLI app's Brocfile
• Creating lockfiles that ember-cli-rails tracks to ensure that requests halt until EmberCLI has had a chance to fully build
• Write build errors to a file so that ember-cli-rails can display them properly