gst/rtp/gstrtph264pay.*: Make it possible to specify profile-level-id and sprop-parameter-sets using properties in ca...

Original commit message from CVS:
* gst/rtp/gstrtph264pay.c: (gst_rtp_h264_pay_class_init),
(gst_rtp_h264_pay_finalize), (gst_rtp_h264_pay_handle_buffer),
(gst_rtp_h264_pay_set_property), (gst_rtp_h264_pay_get_property):
* gst/rtp/gstrtph264pay.h:
Make it possible to specify profile-level-id and sprop-parameter-sets
using properties in case they are not available in-stream.