Added support for playing live streaming content.  Removed TODO in *.h f...

...or is_live boolean.  Added BAD_REQUEST as another return code to issue second HEAD request due to live streaming.  Added limited_time_seek as an indicator that time seeks are supported.  Added dlna_src_is_live() which will check if s0 and/or sN are increasing which indicates live content.  Added logic to not set content size since it is unknown for live content.  Set flag that time seek was received when available range header is provided.