owselectcolumns: Ensure acceptable types
owselectcolumns: Ensure acceptable types

Ensure the Feature and Target views do not accept non primitive
variable types from drag/drop events.

marinkaz/orange3,marinkaz/orange3,kwikadi/orange3,kwikadi/orange3,kwikadi/orange3,kwikadi/orange3,marinkaz/orange3,marinkaz/orange3,cheral/orange3,kwikadi/orange3,kwikadi/orange3,marinkaz/orange3,qPCR4vir/orange3,qPCR4vir/orange3,cheral/orange3,qPCR4vir/orange3,qPCR4vir/orange3,cheral/orange3,qPCR4vir/orange3,cheral/orange3,cheral/orange3,qPCR4vir/orange3,marinkaz/orange3,cheral/orange3