update fit functions with new base objects

in lnProbVMapModel:
    replace obs pars with observation object
    move calls to evaluate model observables to model.updateObservable
        (simplifies chisq_like calculation)

in vmapFit:
    replace obs pars with observation object
    remove dataVector setup (see Observable.defineDataVector)
    clean up addNoise since dataVector is defined

in fitObs:
    update with observation arg and pass to vmapFit