Plot Noise per Line in iTool

This (not available in spectrum mode, or in Virtual Machine mode) will plot the average power spectrum per scan line in an iPlot window. This is mainly useful to check the noise pickup from the power lines on the segmented silicon detector. The power spectrum is plotted versus temporal frequency, not spatial frequency (they are related through pixel size and dwell time). Therefore, this plot makes only sense if the pixel dwell time is constant over the scan line, i.e. if the fast axis device is a piezo.