document new topology "Neutron with NSX"

- add image to Reference architecture that show how new topology looks
  like
- update screenshot that reflects new topology in environment creation
  wizard
- describe new topology in Planning guide
- in User guide mention that we have five available topologies
- explicitly state that separate Physical network is not required for
  "Neutron with NSX" topology

Implements: blueprint vcenter-documentation-update-fuel-5.1
Change-Id: I4b102e41713712c9cb6ce5603c3cd648cd0e9aab