Restrict "Open Package" to MCX content only
Restrict "Open Package" to MCX content only

- Issue MatterHackers/MCCentral#3097
Open Package should only be enabled on MCX selections

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