Swatch

I worked on this update a while ago and I thought I would share. I tried to respect the code style as much as possible but feel free to edit my code to suit your style. I've done my best to follow your guidelines (grunt, test, docs...).

You can now pass a `swatch` option with an array of colors. It will generate a swatch in the color picker. It is useful to suggest default colors to the user.

I also added a method so you can `setSwatch` later on.