Internet Explorer fix for UI.Number and UI.Integer slider.

**Issue:**
In Internet Explorer the "slider" function of both Number and Integer class doesn't work as properly due to event objects in IE not having the proper movement data compared to Firefox & Chrome.

**Solution:**
Implemented similar fix to TransformControls using a previous and current pointer positions. Maybe there is a better way to do this but I was unable to find the correct movement property on event objects in IE. I assume they don't exist after my research.

**Tested on the following:**
Both Win 7 and Win 8.1
Chrome 30
Firefox 24
IE 11


**Note:** I didn't test below IE 11 since previous versions don't support webgl.