Add initial Engine scaffold

[bensheldon]

Does nothing useful except set up a mountable engine and system tests.

Connects to #23

• Creates a separate isolated GoodJob::Engine class so that it is not eagerloaded and GoodJob can be used in situations where loading all of Rails is not necessary.

For installation:

• Add require "good_job/engine" to config/application.rb beneath Rails
• Mount the engine: mount GoodJob::Engine => "/good_job"

New Assets:

• Bootstrap Reboot (MIT License)
• Chartist.js (MIT License)

Note: The current state of asset compilation and gems is up in the air. Given this is a private dashboard, I made the decision to inline the assets into the HTML.