Removing a marker makes the distance matrices no longer valid

Now that we have split the functionalities of
'm_distanceMatrix.getDistances(m_markers)' and
'm_distanceMatrix.calculateOptimalRoute()' it _does_ matter.

The information in the distance_matrices stays relevant, but the
information of m_markers passed on to m_distanceMatrix has changed.
Bug fixed: after drag/drop the markers have to be reordered before they
can be correctly removed