BUGFIX: repair the regression causing low/medium quality songs to be unplayable

* Changed to the old xbmc.player syntax specifying the player type (eg, now
  using "xbmc.Player( xbmc.PLAYER_CORE_MPLAYER ).play( url, item )")
* NOTE: prior change to "xbmc.Player().play( url, item )" was suggested by the
  XBMC team, but causes .mp4 files to be unplayable with codec errors

* Thanks to Nikolas Garofil for taking the time to help me find the proxy and quality issues