logical. False = hide column, True = show column.
Shows or hides a Grid column.
If 'showHide' is true, the column is shown (if it was hidden by a previous command that called this method to hide the column).
If 'showHide' is false, the column is hidden. 'columnName' is the name of the column, and it must be UPPERCASE. Spaces in the 'columnName' must be replaced with underscores. For example, hide the 'LASTNAME' column.