get_trial_wanted_items: Returns list of correct items from a trial
In BrainVR/brainvr-supermarket: Analysis of supermarket data

this function became necessary when the entire structure of the task changed and suddenly the list of items is no longer serialised and is generated but never noted what those items are.

This function requires both actions and results log to be present because it needs both to "deduce" which items were supposed to be collected. In case the tasklist is present, the items are collected from the tasklist instead

1	get_trial_wanted_items(obj, i_trials)

i_trial

because if the item is dropped and then picked up again,
it is considered "Right" again we need to remove wrongly dropped
This is here because the setdiff unique breaks in case
one of the vectors is length 0