Briefly show line of sigth for radius ruler in distance-only mode

[sonora]

Small improvement request from a user regarding our existing feature Configure screen / Radius ruler, for the display mode where the radius circles are not shown, i.e. where the widget just shows the numerical distance between the current position and the screen center.

The user would in that case, on the map, like to see the line of sight drawn between the current position and the screen center. I think this would be a helpful improvement, e.g. for geocachers or hikers, like to identify mountain peaks via their line of sight.

In order to avoid having yet another widget mode, I suggest we could (if the radius ruler widget is active in that mode where the circles are not shown) simply draw the line after every map panning operation for say 5 seconds, then hide it again.

[vshcherb]

I think I got the idea though line is rather heavy looks like. I think it already works when you pan a bit (and move so it doens't trigger long tap) it shows the line and distance between finger point and my location

[vshcherb]