Added setting of minimum and maximum curves values on the graphs

[demvlad]

Added setting of minimum and maximum values of curves on the graph. The revision is fully compatible with the previous scaling method.

To use it, you need to:

Open "Configure graphs" dialog box. Check new "MinMax" checbox on curve settings. Set required values for minimum and maximum chart values for curve (there are real min max values as default). You need to input min and max values in primary units as in logfile. You can look it at default min max values in text fields, Click "Save changes". This is the most versatile way to configure curves. If it is necessary to plot some curves along the same axis, then you need to set the same or proportional ranges of values for them.

With unchecked "MinMax" checkbox the curve scaled in the standard way, as before.

There is a first step for improvment of curve scales. It will be improved in the future. For example, it will be possible to automatically combine several curves on one axis.