The entire Medford Housing Authority board as well as the city’s mayor called on housing chief Robert Covelle to resign Wednesday as still new revelations emerged in a scandal that has engulfed the agency for weeks following reports of favoritism in hiring and contracting. “I strongly believe that it is in the best interest of the Medford Housing Authority and the citizens of Medford that you resign,’’ Mayor Michael J. McGlynn wrote in a letter sent to Covelle.