Fix VALUES and column aliases in CTEs

[georgestagg]

Allows for queries of the form,

WITH t(value, label) AS (
    SELECT * FROM (VALUES
        (70, 'Target'),
        (80, 'Warning'),
        (90, 'Critical')
    )
)
SELECT Date AS date, temp AS temperature
FROM ggsql:airquality
WHERE Month = 5

VISUALISE 
  DRAW line MAPPING date AS x, temperature AS y
  DRAW rule MAPPING value AS y, label AS colour FROM t

which are useful in sqlite.

[thomasp85]

LGTM - we are however venturing into SQL territory that I rarely visit