refactors stats and optimizes js

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

app/views/admin/stats/show.html.erb

@@ -0,0 +1,27 @@
+<% content_for :head do %>
+  <%= javascript_include_tag "stat_graphs", 'data-turbolinks-track' => true %>
+<% end %>
+<div class="stats row-full">
+  <div class="row">
+    <div class="small-12 column">
+      <h2>Stats</h2>
+
+      <div class="small-12 medium-6 column">
+        <h3>Visits</h3>
+        <%= visits_chart_tag id: "visits" %>
+      </div>
+
+      <div class="small-12 medium-6 column">
+        <h3>Combined</h3>
+        <%= events_chart_tag @event_types.keys, id: 'combined' %>
+      </div>
+
+      <div class="small-12">
+        <% @event_types.each do |event, count| %>
+          <h3><%= event.titleize %> (<%= count %>)</h3>
+          <%= events_chart_tag event %>
+        <% end %>
+      </div>
+    </div>
+  </div>
+</div>