Added PlotOptionsFlags class.

This will handle the options available here:
http://api.highcharts.com/highstock#plotOptions.flags
Added PlotOptionsGauge

This will contain the options here:
http://api.highcharts.com/highcharts#plotOptions.gauge
Fixed PlotOptionsFlags

Removed Id from series and made members of PlotOptionsFlags public.
Added a Flag data type.

The type is not included in the reference docs, but in the general documentation:
http://docs.highcharts.com/#flagseries
Added a direct assignment for the flag data.