Use chartkick globally

* Clean up legacy charting imports
* Update existing donut and line charts
* Create helpers for parsing out existing chart data
* Move chart partials to a more common path

spec/models/comment_spec.rb

@@ -5,8 +5,12 @@ require 'spec_helper'
 describe Commercial do
 
   describe '.find_since_last_login' do
+    let!(:user) do
+      create(:user, last_sign_in_at: nil)
+    end
+
     it 'returns none if last_sign_in_at is nil' do
-      expect(Comment.find_since_last_login(create(:user))).to eq(Comment.none)
+      expect(Comment.find_since_last_login(user)).to eq(Comment.none)
     end
   end
 end