Add code to pick marker (actor)
Replace vtkPropPicker with vtkPointPicker in order to get point data

Point data "InputPointIds" identifies which point was picked
Make vtkMapMarkerSet internal to vtkMap
Add marker picking to weather station app
Refactor weather station code to now store station info

Includes adding StationReport class
Can now retrieve station data when marker is picked (!)

Also added code for vtkMapMarkerSet::RemoveMapMarkers()
Add picker to vtkMap, which simplifies logic in application code