Certain American impulses, it may be comforting to know, are flourishing in the midst of the Watergate malaise. The entrepreneurial spirit, for example. Three Chicago businessmen are now marketing engraved Watergate bracelets modeled after the P.O.W. bracelets so many Americans wore before the prisoners' release from Communist jails. The current P.O.W.meaning "Prisoners of Watergate"bracelets carry the names of former presidential advisers and the dates they were indicted or resigned. So far, there are four choices: John N. Mitchell (5-10-73), John W. Dean III (4-30-73), H.R. (Bob) Haldeman (4-30-73) and John D. Ehrlichman...