[Fix/Change] importDfequery: proper handling of missing codes (from sas)

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Add] upperfirst

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Add] ismemberb: block processed ismember

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Fix] setVariableNames: error if first input not table/dataset

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Fix] unid2permno: allow unmatched UnID

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>
[Change] overnight returns #01

Signed-off-by: Oleg Komarov <o.komarov11@imperial.ac.uk>