Don't allow users to run >2 iterations when applying model in ar_only mode

[calebweinreb]

When running "apply_model", the number of iterations should be at most 2. Anything more than that is redundant. Maybe we should display a warning (and override the user input?), or raise an error?

[hummuscience]

Does that mean that the default (500) is far too high and should be set to 2?