Systematic definition of thresholds

Moved threshold definitions to a separate file: wlt/config/analyzer_regions.py.
Implemented automatic calculation of thresholds based on statistical distributions: --stat_regions option.
Implemented summary plots for DAC and Ring Oscillator calibrations: -p -2 option to include them.
Added GND subtraction in ADC calibration curves.
Added information about the test to the summary page.
Minor bug fixes.