UPDATE: add HACK to allow scrobbling

Added fictional duration to songs as a HACK to enable scrobbling

* scrobbling doesn't work with the current XBMC core player unless the
  'duration' field of the song info is set prior to starting the song
  (even though the song duration will be correct in the player)
* with no 'duration' (or 0 or -1), last.fm sees the song playing but
  never receives the final scrobble notification to add it to the history
* BUG: the HACK does cause the core player to see/display an incorrect total
  song time (although the progress/duration bar is visually correct)

NOTE: scrobbles are cached until script execution is halted and then submitted en mass

NOTE: (see URLref: http://www.last.fm/api/scrobbling) for scrobble info