Double click fire back on single touch click (touch monitor)

Sample Demo: [videoDemo.zip](https://github.com/AnalyticalGraphicsInc/cesium/files/2653272/video_bugDoubleClickFiredOnSingleClick.zip)

A bug on cesium viewer on touch monitors. Which double click being fired by each single touch click on the viewer.

As shown in the video, I attached a simple listener to the document to print ( hello dblclick ) if a double clicks triggered.

(0:00 to (0:27) Just demonstrated mouse double click works fine.
At time (0:27+) I double clicked using touch on the shuttle ring (HTML element) bottom left of cesium page, and then I single touch clicked on the viewer which then you will see on console that ( hello dbclick ) being called for every single touch click on viewer.

This bug could be also initiated on any HTML component like ( e.g. buttons in toolbars ) when using touch screens.

Tested on Chrome.

Start by reproducing the attached video scenario in Chrome: double-click an external HTML element on a touch monitor, then single-touch click the Cesium viewer. Trace the viewer's touch and double-click event handling, and consider the issue done when each subsequent single touch produces only a single-click event and the existing mouse double-click behavior still works.

Written by the indexing model from the issue text.