Two leaders at the state House are proposing a statewide sales tax holiday in August to stimulate the local economy.  House Speaker Robert DeLeo and Ways and Means Committee Chair Brian Dempsey released a joint statement Wednesday advocating the proposal.  State lawmakers are set to debate the matter today as part of a jobs bill.  The tax holiday would fall on August 11th and 12th.  The House leaders say they want to support local businesses and help keep jobs in Massachusetts.  No item over $2,500 would be included in the holiday.