Add HorizontalTag for custom arrow style
Add HorizontalTag for custom arrow style

- Issue MatterHackers/MCCentral#3002
Layer indicator should have arrow pill background, use small font

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