'plotselect' feature in SCAN_DISPLAY
(follow up of #245 (closed))
SCAN_DISPLAY needs to be enhanced to allow selection of data to be displayed by flint while a scan is running, like
plotselect function of Spec (but on steroids !).
Test to do: if scans from ID11 (interlaced, piezoscan, cscan_time, cscan_pos...) can be visualized as expected once user defines what to plot