Added the ability to have text show on the color picker button

I need to show a bit of text on the color picker button, so I added the functionality into this script. The text is loaded from a data- attribute when `colorPicker()` is called. The button ends up looking like:

![Screen Shot 2013-04-07 at 11 02 09 PM](https://f.cloud.github.com/assets/509837/348773/84caecb2-9f83-11e2-807f-14933a7f5033.png)

Contributing it back in case this is something you'd find useful. I haven't updated the minified js file - let me know if you'd like me to.