The Position Marker Settings dialog

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

(might already be submitted to Marble trunk by the time this task is started) should get extended to provide settings for:

* scaling the position marker (using a slider: 0.25, 0.5x, 1x, 2x, 4x, allowing for smooth in-between values).

* Making Colors configurable for the

   - Accuracy Circle

   using buttons which have the color as a background value and the label beside. A click on the button would trigger the appearance of a QColorDialog. The button should go into a dedicated groupbox labeled "Colors".

This task includes creation of the required backend implementation that is needed to provide a scalable position cursor and the color configurability of the accuracy circle.