Refactor charts.Bar to use plot.xts

[erichung0404]

Core functionality

• plot bar charts in multiple panels using multi.panel=TRUE argument in plot.xts.
• panels share the same range of y axis using yaxis.same=TRUE in plot.xts.
• some arguments of plot.xts such as yaxis.right, yaxis.same, up.col and dn.col can be passed to charts.Bar to control the range of y axis of each panel and color of positive and negative bars in ....