Dashboard stats

PT story: https://www.pivotaltracker.com/story/show/64726524
Screenshot: 
![image](https://cloud.githubusercontent.com/assets/1007981/4091279/dcd318aa-2f86-11e4-9b60-8ed0f335440e.png)


Changes:
• dashboard controller
• statistics concern
• dashboard view
• link at bottom of global footer
I don't want to be a pain but... this doesn't actually remove it from the global scope. Class definitions are always global. As a test, use the equivalent statement:
~~~ruby
FakeController = Class.new(ActionController::Base) { include Statistics }
~~~
You will see multiple warnings like:
~~~
spec/controllers/concerns/statistics_spec.rb:5: warning: already initialized constant FakeController
spec/controllers/concerns/statistics_spec.rb:5: warning: previous definition of FakeController was here
~~~
The reason no warnings cropped up with your implementation is because this statement is equivalent to reopening the class and including the `Statistics` module again and again. If you are willing to investigate further, you should find that you will be able to access the `FakeController` in a later spec. My suggestion would be to refactor the `before` and `let` statement into just one `let` statement:
~~~ruby
let(:fake_controller) { Class.new(ActionController::Base) { include Statistics } }
~~~