This task is about creating a Position Marker trail for the Position Marker Plugin in Marble and its settings dialog:

http://svn.reviewboard.kde.org/r/6232/

A checkbox on the settings dialog should be created in the UI file that enables and disables a trail left behind the position marker:

[x] Trail

The position trail should consist of several circles that are position in the last few positions that are different from the current position. (They should not show up if the position reported hasn't changed). So the circles should mark the last 5 different positions that have been reported by the position backend. The size of the circles should get smaller and the color should become more transparent the older the trail points get (resembling a "fade out" or a kind of comet tail basically).

The color should be configurable using a QPushButton with a background that has the color of the trail as a background. A press on the button should make a QColorDialog pop up. In the positionmarker settings dialog this button would appear together with other color settings in a dedicated "Color" group box.