Add HorizontalSpacer to the ignored types list
Add HorizontalSpacer to the ignored types list

- Issue MatterHackers/MCCentral#3031
Empty item in overflow list

larsbrubaker/MatterControl,jlewin/MatterControl,larsbrubaker/MatterControl,unlimitedbacon/MatterControl,unlimitedbacon/MatterControl,jlewin/MatterControl,unlimitedbacon/MatterControl,unlimitedbacon/MatterControl,mmoening/MatterControl,jlewin/MatterControl,mmoening/MatterControl,mmoening/MatterControl,jlewin/MatterControl,larsbrubaker/MatterControl,larsbrubaker/MatterControl