By Tom Verducci Both sides left so frustrated that the talks themselves are in jeopardy as Monday’s deadline looms. On the day after progress was made on a side issue, baseball owners and players proved again Saturday what happens when they try to touch core economic issues: anger. Both sides made package proposals Saturday that led to so much frustration that the talks themselves joined Opening Day as jeopardized. The players began the day by making their most comprehensive proposal, which included their first movement on the competitive balance tax since the owners began the lockout Dec. 2. …