Incremental logging trace drawing

[M4rtinK]

As long as projection does not change (zoom in/out) and nothing else needs to be redrawn it might make sense to draw the logging trace incrementally - one line segment at a time, without clearing the canvas in between.

It's possible there might be issues with:

• separate segments logging worse than polyline drawn with line_to() and then stroke()
• we need to watch for other canvas users (route) becoming visible during incremental drawing