Added YAML data fixture for populating an intiial database.

### What is the problem / feature ?

Adding all of the shift data by hand with the admin would take too long.

### How did it get fixed / implemented ?

I created a YAML data file as a fixture. 

### How can someone test / see it ?

Once you've installed PyYAML, you can try:
python manage.py loaddata sample_data

Note: this will overwrite existing data...

![odd](https://cloud.githubusercontent.com/assets/611731/2556031/df2db83e-b6c9-11e3-8a9b-a50e93f9d591.jpg)