* [LIQ] Add more tests for builtin aggregates Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz> * [LIQ] Add `first`, `last`, `mode` and `median` aggregates and `group_concat` alias Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz> --------- Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>