model.update should happen in place

[jeremymanning]

To update a model, we currently use updated_model = model.update(bo)

However, this should happen in place-- i.e. by default model.update(bo) should return None, and instead should modify model in place.

If it's useful to have the non-in place syntax, we could set an inplace flag (default = True) like for pandas dataframes, and allow the user to specify inplace=False if they want to use the current syntax. (That would return an updated model object, but would not change the original object.)

[andrewheusser]

@lucywowen - i'm happy to tackle this one, but not sure if it will mess up your analysis pipelines...