Dlnasrc 106 memory leak

Changed dispose() to finalize() as recommend in GStreamer code review - dlnasrc #40.  Renamed dlna_src_head_response_free() to dlna_src_head_response_free_struct() to align better with _init_struct().  Reviewed all "new" calls and verified that there were associated "free" calls.  Got rid of unnecessary calls to dlna_src_uri_init() to make logic cleaner.