Celery and other stuff

I've restructured a little bit the module, so we can plug in another distributed tasks manager if we want to, the module looks like this now:

```
distributed
├── __init__.py
└── celery
    ├── __init__.py
    └── tasks.py
```

* The `ngi_server.py` script is the worker process that will be running in the login node in UPPMAX
* The `redis_to_celery.py` script is a script that will be running in the background (or as a cronjob) and will execute Uppsala tasks

Everything works, but I need to make it more configurable (localhosts and ports harcoded == shame). But I think that this small PR is okay, and actually doesn't interfere with other code.

I'll open issues for the things I need to fix now.