#314 Add SVG element hinting for more renderers

[Scott Dudley]

This patch adds SVG element hinting support to:

• PiePlot and MultiplePiePlot
• AbstractCategoryItemRenderer
• BarRenderer
• StackedBarRenderer
• AbstractXYItemRenderer
• ClusteredXYBarRenderer
• DeviationRenderer
• StackedXYAreaRenderer
• StackedXYBarRenderer
• XYBarRenderer
• XYLineAndShapeRenderer

Some of the existing renderers have been adjusted to call an overridable superclass method with references to the current series/row/column/etc index, as well as a reference to the dataset, in order to begin an element hinting group. This makes it easier for clients to subclass the renderers and provide a different format of ItemKey than the default.

In AbstractXYItemRenderer, we also use the "addEntity" method (which was originally designed to add data to the EntityCollection) to also draw a transparent hotspot of the same shape in the SVG. I am open to refactoring this logic if you care to suggest guidance on how you would like it done.