[Sprint #4] Integrate with Celery

> Hello, @darjeeling. Would you please help me with test celery ? ( i have no idea with testing celery with UnitTest )

### Summary
- i have integrated `Celery` and `django-celery` with our project.
- i have NOT tested with test cases. because i don't have any idea testing tasks with worker
- i have NOT included any test cases, BUT i have properly tested `Celery Worker` working with tasks and message queue. ( please see results below. )

### Celery Settings and tasks
- in this case, i have tested with `scraper_example` task.

![screenshot 2014-08-19 17 01 46](https://cloud.githubusercontent.com/assets/4688315/3963180/7aed04f0-2777-11e4-9ede-3ff457d6dfe0.png)
![screenshot 2014-08-19 17 01 50](https://cloud.githubusercontent.com/assets/4688315/3963181/7aed7656-2777-11e4-98b7-33cb32792adf.png)

### CeleryWorker Results
![screenshot 2014-08-19 17 02 14](https://cloud.githubusercontent.com/assets/4688315/3963182/7af15352-2777-11e4-92b9-4ab451781d7a.png)

### CeleryBeat : periodically sending message to RabbitMQ 
![screenshot 2014-08-19 17 02 29](https://cloud.githubusercontent.com/assets/4688315/3963183/7af5057e-2777-11e4-8be6-516731f60939.png)