Create ItemRangeOverflow item type

Overflow simply extends ItemRange with a new getWidth() function that
determines if the content of the range is wider than the range box
itself.

This did require adding a getWidth() function to the Item object that
always just returns this.width, and adjusting Stack.js to use the new
getWidth() function instead of item.width

Custom time bar as a component

Conflicts:
	vis.js
	vis.min.js

Current time bar as a component

Fix dataSet parsing of Moment objects

Calling just moment.clone() won't do anything but error. Since moment.isMoment(object) guarantees object is already a moment instance, just calling moment(object) will clone
it per the moment docs http://momentjs.com/docs/#/parsing/moment-clone/

object is already a moment instance. Calling moment(object) will clone
it per tehe moment docs http://momentjs.com/docs/#/parsing/moment-clone/

Update references to moment.js in the examples