This task is a preparational task for improved angle measurement and polygon area calculation inside Marble's measure tool. Because of that the task should be submitted for review but it shouldn't be submitted to the repository unless the follow-up-tasks are completed. Please point this out in the commit message.

Add another option "Bearing Change" to the Settings dialog of the MeasureTool. It should display the difference between the bearing of the current segment and the previous segment:

currentBearingChange = currentBearing - previousBearing.

Hence the first lineSegment should not show a currentBearingChange value.

For now the value should be added to the same place where the other values (distance and bearing) are displayed. It should always be added as the last value. In a follow-up task we will make this more graphical.