flys/issue903: Display the discharge tables of the selected gauge as chart in historical discharge calculation. There is a new class 'DischargeTablesChart' which is a Canvas and displays the chart using the new service 'DischargeTablesServiceImpl'.

SYMBOLSET
SYMBOL
  NAME 'point'
  TYPE ELLIPSE
  POINTS
    1 1
  END
  FILLED TRUE
END
SYMBOL
  NAME "square"
  TYPE VECTOR
  POINTS
    0 0
    0 1
    1 1
    1 0
    0 0
  END
  FILLED TRUE
END
END