Refactor reChart function to make plot_object settings changeable

[erichung0404]

reChart function is the base function called by zoomChart() and zooom(). Since plot_object$subset didn't seem to work for plot.xts based object, special handling is provided to fix unequal length issue and make x-axis and y-axis value changeable. The issue occurs in xts:::chart.lines() function which calls lines() to draw original price series for x by plot_object$Env$xycoords$x and the subset series for y. So it throws error: "'x' and 'y' lengths differ." See issue joshuaulrich/xts#146 for more detailed information.