save inputs to json selectively

[pedroliman]

only save natural history inputs for the natural history design and only save screening inpugts for the screening design.

[carolyner]

Note that the natural history parameter, p, which determines the shape of the Richard's growth curve, is required for screening. Otherwise, NH parameters are not needed during screening.

[pedroliman]

natural history parameters will always be available when running the screening - we're just no longer saving these parameters to the json object that is used for screening runs. These parameters will be already available elsewhere (in the model and in the natural history experimental design file).

now we can run:

model$to_json(input_types = "nh") # for natural history
model$to_json(input_types = "screening") # for screening inputs
model$to_json(input_types = c("nh", "screening")) # for both
model$to_json() # for all available input types both