[CombinedChart] Grouped Bars + line chart

[liuxuan30]

Looks like we don't support grouped bars + line chart tegother?

Say I have 3 bars on each xIndex, but only one line dot on each xIndex.

[danielgindi]

PhilJay/MPAndroidChart#449

[liuxuan30]

I was thinking to assemble the bar chart views and line chart views together as sub views, and then I was thinking only using renderers, and you actually implement it this way.

It seems like the main problem is the combined chart does not call BarChartView.calcMinMax() to recalculate the _deltaX and then the grouped goes wrong, and the line chart and other charts cannot use this _deltaX for themselves.

[danielgindi]

Btw this is a duplicate of #169 :-) Closing...