Make only intended charts draggable

On a page with other charts, this plugin seemed to reduce the chart padding with the `chart.redraw()` line, and made columns have a dotted border if the values were near 0 (which should happen on draggable charts).  I think if you want to have a draggable chart, you shouldn't have to have these events and styles affect other charts.

![badpadding](https://f.cloud.github.com/assets/1410985/1935380/f3dcb4f0-7ef8-11e3-9636-c2b9193b3cad.png)
Above is some non-draggable charts with `chart.redraw()` triggered.

![betterpadding](https://f.cloud.github.com/assets/1410985/1935386/02c5c5ba-7ef9-11e3-8bdf-d5473c95c042.png)
And without `chart.redraw()` in the draggable-points plugin.  Note the dotted columns in the column chart are still there without the `drawTracker` fix.