EPD-190: Small tweaks and javadoc
EPD-190: IAisLayerCommonSettingsObserver now inherits from IVesselLayerSettingsObserver instead of ILayerSettingsObserver.
EPD-190: Javadoc for IVesselLayerSettingsObserver
EPD-190: Fixed AisLayerCommonSettings such that it inherits from VesselLayerSettings instead of LayerSettings.
EPD-190: Added callback handlers for IVesselLayerObserver in AisLayerCommonLocalSettings