fix: [stix import] Fixed issues with additional namespaces
fix: [stix import] Fixed issues with additional namespaces

- Using a list where any additional namespace can
  be added
- Catching any missing additional namespace with
  the return code '4' raised in case of namespace
  not found error

SteveClement/MISP,SteveClement/MISP,FIRSTdotorg/MISP,MISP/MISP,MISP/MISP,FloatingGhost/MISP,MISP/MISP,SteveClement/MISP,FIRSTdotorg/MISP,FIRSTdotorg/MISP,FloatingGhost/MISP,FloatingGhost/MISP,MISP/MISP,MISP/MISP,FloatingGhost/MISP,FIRSTdotorg/MISP,SteveClement/MISP,SteveClement/MISP