Tracer Model P1.1 - Signify the direction of time

[dloch]

Find a way to signify the direction of time in the connection between data points. As this already looks a bit cluttered, try to avoid adding more lines.

During this, the look of the lines should be adjusted to avoid confusion with other lines that are added -- specifically the displayed image lines.

[dloch]

Lines are now shaded according to the selected color scale -- Bottom of the scale is earlier, top of the scale is later. This may need a minor adjustment when the colorscale variable is selectable.