add iterations capability to SAM and SPiCT

Hi Simon,

We just noticed that the FLStock output from SAM2FLStock didn't have the plusgroup defined. I tried this on your example and find the same:

library(FLfse)
fit <- FLR_SAM(stk = cod4_stk, idx = cod4_idx, conf = cod4_conf_sam)
stk <- SAM2FLStock(fit)
range(stk)
# min       max plusgroup   minyear   maxyear   minfbar   maxfbar 
#   1         6        NA      1963      2018         2         4 

I think this would provide the information about whether this should be defined or not: fit$conf$maxAgePlusGroup

Thanks,
Marc

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