implement token bucket rate limiting

app/views/static/too_many_requests.html.erb

@@ -1,2 +1,2 @@
 <h1>Too Many Requests</h1>
-<p>You can only make <%= CurrentUser.api_hourly_limit(false) %> updates and <%= CurrentUser.api_hourly_limit(true) %> reads per hour.</p>
+<p>Please rate limit yourself</p>

app/views/users/_statistics.html.erb

@@ -153,6 +153,14 @@
             (<%= link_to "help", wiki_pages_path(title: "help:api") %>)
           </td>
         </tr>
+
+        <tr>
+          <th>API Limits</th>
+          <td>
+            <%= CurrentUser.user.remaining_api_limit %>
+            / <%= CurrentUser.user.api_burst_limit %>,
+          </td>
+        </tr>
       <% end %>
   </table>
 </div>