remove erroneous samples

session 342, chs 15 & 38: erroneous values in NumValSamples
specified root_nse_folder
write only correct samples to new .ncs file

session 342, chs 15 & 38: erroneous values in NamValidSamples
retrieve .nse file names for 'standard' sessions

Representative sessions are always selected from the set of non-roving
stimulus sessions. Thus, whether the session to be processed is
non-roving or roving, the standard with which it is compared is always
taken from a non-roving session. This requires modification of the
folder-finding function, to return a non-roving session.
always return a non-roving session as 'standard'

Representative sessions are always selected from the set of non-roving
stimulus sessions. Thus, whether the session to be processed is
non-roving or roving, the standard session returned is always a
non-roving session.
specifically return (non-roving) standard session