Routing: add support for waypoints

[Martin Kolman]

• waypoints = desired points which the route must go through
• add waipoint button to the on-screen menu for routing
  • only show it when applicable (after both start and destination are set)
• number the waypoints after adding them on the map
• waypoints should be dragable
• draw a remove button next to each waypoint (only after clicking it + timer ?)
  • re-number waypoints once one is removed
• waypoints should be visible even after a route is found (but should not be clickable/dragable)