mpegts: Add support for creating a NIT section

Functions that will enable user to create Network Information Tables.
mpegts: Add network name descriptor construction

Add function to create a Network Name DVB descriptor.
mpegts: Add program_number to GstMpegTsPMT
mpegts: Add support for creating PAT/PMT
mpegts: Support parsing of DVB Teletext descriptor

Descriptor tag is 0x56
mpegts: Add creation of DVB Subtitling descriptor

Descriptor tag is 0x59
mpegts: Support registration and custom descriptor

Support for registration descriptor (0x05)
Add function to create a descriptor with custom tag and data
mpegtsmux: Add support for muxing SI tables

The muxer is now able to include DVB sections in the transport stream.

The si-interval property will determine how often the SI tables are
muxed into the stream.

The section is handled by the mpeg-ts library. Below is a small example
that will include a Netork Information Table with a Network Name
descriptor in the stream.

GstMpegTsNIT *nit;
GstMpegTsDescriptor *descriptor;
GstMpegTsSection *section;
GstElement *mpegtsmux;

gst_mpegts_initialize ();

nit = gst_mpegts_section_nit_new ();
nit->actual_network = TRUE;

descriptor = gst_mpegts_descriptor_from_dvb_network_name ("Network name");
g_ptr_array_add (nit->descriptors, descriptor);

section = gst_mpegts_section_from_nit (nit);

// mpegtsmux should be retrieved from the pipeline
gst_mpegts_section_send_event (section, mpegtsmux);
gst_mpegts_section_unref (section);
mpegtsmux: Use mpeg-ts lib for PAT/PMT sections

Rewrite of the PAT/PMT section handling to use the mpeg-ts library
mpegts: Updated docs with new API