#33 Integration with Google Calendar

Admin can import vacations from Google Calendar.
When user creates, updates or deletes event, it appears in Google Calendar.
Added tests.
![zrzut ekranu z 2014-09-03 14 06 47](https://cloud.githubusercontent.com/assets/6718923/4133891/8d71772a-3364-11e4-94c9-dd9a2382fb8c.png)

Should be `'calendarId' => AppConfig.calendar_id`