add full set of diboson processes

[mafrahm]

This PR adds all the diboson decay channels, including the VV parent processes.

Open questions:

• should we always be consistent in the order of listing VV decay products (leptons, then neutrinos, then quarks)? This would also be more consistent with DAS conventions
  • example: VV->lnu2q instead of VV -> qqlnu (as it currently is for Higgs + HH(bbVV))