Fix Plotting Issues

[earik87]

There are bunch of things to do with the plot;

• make y axis limits according to the min/max values of the measurement data.
• add axis labes;
  xAxis: Stage movement (in micrometer).
  yAxis: Voltage in Lockin Amplifier.
• When we click on scan button for a second time with a different range, old tick labels are still there. See screenshot.