Allowing slider tray events to propagate and other small tweaks

Initially, this code was created to address #155 "onDragStart events don't fire when dragging slider" However, it turns out that drag events are not firing for another reason entirely that isn't due to an error in our code.

Added example carousel 11, a new carousel that demonstrates how to attach event handlers to the slider tray tag.

Removed stopPropagation() calls from our internal event handlers. Not sure why they were added. Removing these didn't seem to affect the demos. Allowing the events to propagate increases the customizability of our carousel components.

Lastly, I renamed some misleading class method names relating to drag start and end. These methods had nothing to do with React's onDragStart and onDragEnd synthetic events. The names confused developers.