add x axis padding support for date
fix stackable chart elastic padded x axis calculation issue
improve test cases for elastic axis implementation
implement composite axis elasticity

 - add padding for both x/y axis
 - add x axis elasticity
 - add stacked axis x/y calculation logic
 - add composite axis x/y calculation logic
improve bar x calculation to be more accurate representing underlying data
add renderlet to base chart impl
add renderlet hook in coordinate grid chart
move invoke renderlet logic to base chart
add renderlet hook in pie chart impl
add test case for bar chart renderlet hook
add test case for line chart renderlet hook
add renderlet hook in data count widget
add renderlet hook in data table widget
adjust min slice angel allowing label display
extract render() to base chart and introduce doRender indirection
extract redraw() to base chart and introduce doRedraw indirection
introduce renderlet hook

renderlet are custom function hooked into render/redraw funciton of all charts to allow user to implement any kind of custom rendering logic. since its a function invoked by chart as an internal routine, renderlet can also access chart's internal data representation.

 - extracted render/redraw to base chart
 - added renderlet to base chart so it is available on all charts
introduce chart grouping
add chartGroup based anchoring to all charts
implement chartGroup aware rendering and redrawing