Hover legend and interactive legend

Added examples of both a hoverLegend and interactiveLegend. The interactiveLegend could possibly replace both toggleLegend and hoverLegend, but at the moment, it feels a bit clunky, since all I did was copy code over to that class. 
pls name hoverCallback and clickCallback. also, for consistency, maybe it should be toggleCallback instead of clickCallback. this is a bit more descriptive i think