Cleaner LinePlot legends when a single run is in use
Created by: derkling
The legend auto generated by LinePlot contains the "runN:" prefix for each signal. However, this prefix is useful only when multiple runs are actually plotted, for example to distinguish the same signal coming from different runs.
When a single run is considered, the legend is more clean to read if we omit the "runN : " prefix, thus reporting just "event:column" as name of each signal.