EPD-61: Added AIS target map to AisLayerCommon. Implemented methods that subclasses can use to modify the map. These methods make sure that the map remains in sync with the graphics list from EPDLayerCommon.
EPD-61: Removed targets map from AisLayer (ship). Calls that made use of this map now instead use the methods exposed by AisLayerCommon to modify its targets map + graphics list.