scan_preemph: arguments and store/load data

Example:

./scan_premph.py scan -o output_data/DATE_CC_badVideo -c direct -n 150 -s

will:

• scan over all three of TAP0, TAP1, TAP2 using 150 triggers for each set of tap values
• save the data as JSON, e.g. as output_data/2019-03-15_09-39_direct_badVideo.json

./scan_premph.py plot TAP0 TAP1 --fix TAP2=0 -i output_data/2019-03-15_09-39_direct_badVideo.json -o output_data/DATE_XX_YY_FF_CC_badVideo

will not scan but simply plot the data of the JSON:

• output files will be named e.g. output_data/2019-03-15_09-39_TAP0_TAP1_TAP2=0_direct_badVideo_eyejitter.png
• plots will have TAP0 as x-axis and TAP1 as y-axis
• only the data where TAP2=0 is plotted
• if --fix is not specified, a set of 2D plots is created for each different value of the third parameter