Add excluded boolean field and exclude reason string field to StudySubject Model

From Joëlle:

Do you want to distinguish between resigned and excluded?

yes

Or could we consider it as different thing and have separate reasons as well?

Yes. If excluded we want to differentiate if healthy or already demented. We can only take participant with a mild cognitive impairment, not the ones that are healthy and also not the one that already show to much cognitive problems (already demented). So healthy and demented are exclusion factors. However, for the healthy we can offer to retest a year later if they think that they still have problems in reminding things. So would be cool if there a reminder for a follow up meeting could be installed if the neuropsy has hinds that there might be problems later in one years time.