refactors stats and optimizes js

JS libraries for stats (d3, c3, etc.) only load now when needed (stats/show)

app/controllers/admin/stats_controller.rb

@@ -0,0 +1,7 @@
+class Admin::StatsController < Admin::BaseController
+
+  def show
+    @event_types = Ahoy::Event.group(:name).count
+  end
+
+end