Add flag to check whether an item in the Itemset is currently being dragged

It was broken by PR (#1729), which fixed issues #112 & #1730.
As far as I can tell that change shouldn't influence the DataAxis (vertical-axis), but only the horizontal axis.

 @yotamberk can you check if your examples still work as expected?

Internet Explorer does not support the ES6 Number.parseFloat (see http://caniuse.com/#feat=es6-number). Instead, substitute the regular parseFloat method.

Cleanup of linegraph's event handling
Fixed #1557: Make sure we don't default to scientific notation.
Couple of minor fixes in group counts and ranges.

-Keep single defaults location
-Update documentation on formatting function.

Some fixes and cleanups after the large rewrite.

Provide the DataView.map() method similar to the DataSet one.

Fixes DOM API deprecation warning in Chrome.
Please see: https://www.chromestatus.com/features/5724912467574784

This is an improved version of PR #1501.

Minor cleanup

-Draw points in bar icon if appropriate
-Introduce point icon
-Cleanups

Add some enhancements for stacking (especially with regard to shading)

-Never push into arrays that have a known length
-Move more functions back into the main updateGraph method

Fix no-group data input case.

Separate shading from line drawing (fixes drawing order)
Cleanup of draw code
Fix icon-shading CSS override