Adds default fill & stroke colors if none are provided.

If you define anyone of the 6 graph types without adding a color to the data array:
* fillColor
* strokeColor
* pointColor
* pointStrokeColor
* color

![chartjs-nodefinedcolors](https://f.cloud.github.com/assets/71634/760024/d898feb2-e7a2-11e2-8f8d-34ebd4090785.png)


Colors will be created automatically.

![chartjs-randomgraph](https://f.cloud.github.com/assets/71634/760003/24c5beca-e7a2-11e2-9d1c-ae3db6c5206f.png)

These colors are the same for each key in the data array, the opacity is based on the type (stroke/fill/point) and can theoretically scale to any number of colors due to color being derived using a hash of the key.