Implement support for SCTE-35 switching messages.

Implement support for SCTE-35 switching messages.

This module implements a dissector for the main table in a SCTE-35 message, a
splice_info_section. This payload is carried in a MPEG Section Table with a
table ID of 0xFC. PIDs carrying this sort of table are also noted in the PMT
with a stream type of 0x86, and a registration descriptor with fourcc 'CUEI'.

The various splice command types are implemented in separate modules, and are
linked to this dissector through the field scte35.splice_command_type. Field
names follow the conventions documented in the SCTE35 specification.

This dissector does not support encrypted SCTE35 messages, other than
indication through the scte35.encrypted_packet flag.

The SCTE-35 protocol is described by the Society of Cable Telecommunications
Engineers at <https://www.scte.org/documents/pdf/Standards/Top%20Ten/ANSI_SCTE%2035%202013.pdf>.

Bug: 12521
Change-Id: I3113e6e61a4e7f1a4a932a0128ca2846c7ce6e6f
Reviewed-on: https://code.wireshark.org/review/15562
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>