Added missing library features

Implemented the following changes.

- The HighchartsChartObject.series property should return
HighchartsSeriesObject[] not HighchartsSeriesChart[].

- Added missing setVisible(...) overloaded method to the
HighchartsSeriesObject interface.

- Added missing JQuery.highcharts(...) method overload containing
callback function parameter used to manipulate the chart instance.

- Amended test file to exercise all changes in this commit.