Simplify plotMarker.js

`addMarkerToMap`:
* Rename as `onMarkerPlacedByClick`
* Don't export, as it's not referenced externally
* DRY it out by calling onMarkerMoved(), which does exactly what the removed lines do

Also:
* Remove markerPlacedByClickBus (and its exported name markerPlacedByClickStream) are currently unused (`markerPlacedByClickStream` was referenced in addTreeMode.js, but so is `markerFirstMoveStream` and that will
have an event whenever the other would have.)