Participate in event

- イベントへの参加機能追加
- イベント参加機能のテストを追加
- production用にsecret.ymlを修正

![2014-09-04 18 20 01](https://cloud.githubusercontent.com/assets/3064024/4147191/0b5eb070-3415-11e4-9b31-ecbd7e3efe98.png)

```ruby
4.1.4@2.1.2 (main)> ev.participants.count
   (0.1ms)  SELECT COUNT(*) FROM "participants"  WHERE "participants"."event_id" = ?  [["event_id", 1]]
=> 0
4.1.4@2.1.2 (main)> ev.participate_count
   (0.2ms)  SELECT COUNT(*) FROM "participants"  WHERE "participants"."event_id" = 1
=> 0
```
微妙に展開度合いが違う :speech_balloon: