Fast threshold scan

• Implement a threshold scan that searches for the beginning of the S-curve with coarse steps. When the start is found it scans with fine steps until almost all pixels see all injections. This reduces (especially after tuning) the number of steps to sample the pixel response curves.
• Since data has to be quickly histogrammed online a new fast occupancy histogrammer, that can also be used for other tunings, was added. The histogramming is non blocking on another CPU core.
• The scan base can also store arbitrary scan parameters now. That is a much missing feature that should be used by all scans from now
• Performance test with linear flavour and with standard settings:
  • untuned: fast threshold scan loop takes 2 min. and gives < 20 not fitted pixels; threshold scan loop takes 2:30 min and has < 5 not fitted pixels
  • badly tuned: fast threshold scan loop takes 1:15 min and gives < 20 not fitted pixels; threshold scan loop takes 2:30 min and has < 5 not fitted pixels
• Enhance automatic fit range finding for noisy s-curve data
• Enhance S-curve convergence by fixing amplitude

Bugfixes:

• Prevent crash when no maskfile is defined
• Do not use pylab plt for new tot/tdc plots. This triggered warning that more than 20 figures are open
• Fix search for vivado binary

Enhancements:

• Tune TLU does not use pylab for plotting to allow headless usage