Default css + features

Hi I have tweaked few things :
- changed button element to div element, because I noticed some differences in padding between firefox & chrome
- changed default css for styleBtn & styleIcon, because it was broken
- added checkbox-label attribute to bind a clickable label to the checkbox (one way binding so you can pass expressions to this attribute)
- added checkbox-class to add some css classes only to the checkbox "button" without impacting label (one way binding)