FIX update AllocModel.py so calc_evidence template is correct.

1) In AllocModel.py, the template method for calc_evidence() needs to be updated. The base method only takes self as an argument, but it's called from (for example) Hmodel.py line 118 as allocmodel.calc_evidence(Data, SS, LP). I don't think this will ever cause crashes, it just makes it confusing to design your own subclass of allocModel if the base class isn't fully specified.