draggable WPs & bugfix useAsWaypointButton

feature: draggable waypoints
the user can drag waypoints on the map (causes re-calculation of the
address representation in the DOM elements as well as re-calculation of
the route)

bugfix: useAsWaypoint buttons caused errors
bugfixes for waypoints

bugfix: addingWaypointByRightclick: increment number of next unset
waypoint

bugfix: removing wayoints: first two waypoints remain visible but marker
and address are removed
bugfix: route instructions

route instructions are removed if the route is re-calculated and cause
no more errors