Date base is taken into account for date formulas

Date base (1900 or 1904) wasn't taken into account in read-cell for
formula date cells.
Now it's fixed. read-cell-value for Cell/CELL_TYPE_NUMERIC doesn't use
date-format? internally, but isn't removed to save backward
compatibility.
However read-cell-value itself doesn't consider date base as it isn't
present in cell value and requires changing method args.