[Rivet] MC_* analyses

[Frank Siegert]

Hi Riveters,

We seem to have some duplication in the MC_* analyses, e.g. between the 
MC_ZJETS and MC_ZANALYSIS, both of which look at Z and jet observables.

Can I merge the latter into the former? I would at that time drop the not-
Z-specific stuff like charged particles multiplicity. I think this would 
belong into a separate MC_* analysis which can then be run on top of that 
one if desired (as opposed to the jets observables, which are correlated 
because of the removed Z).

I would like to do something similar for MC_WANALYSIS -> MC_WJETS, which 
doesn't yet derive from MC_Jet_Analysis, and thus misses out on some neat 
jet observables implemented there (and duplicates the simpler ones 
anyway).

Cheers,
Frank