Removed unused var
MonthlyAverageGraph: Compute averages, minimums and maximums
Prepared more tests
Removed unused var
Just use Collectors#summarizingInt
Added crosshairs option
Make series contain arbitrary values (especially arrays of numbers)
Added valueSuffix
Created plotline class

Add plot lines to axxises
Created marker class

Configure the marks of highcharts
Added various new attributes
Manage additional plotlines
Display monthly average
Worked on monthly average
Added missing tests for series
More crosshairs
Added missing tests for ToolTip, removed unused method
Added missing tests
Added missing tests for PlotLine
Added missing tests for Marker