dvb: fix mistake in NIT processing.

This was stopping some DVB-C networks from being properly scanned.
Added initial support for transcoding.
Parse the audio_type field of the iso639_language_descriptor - this indicates if the audio stream contains audio description for the hard of hearing.  Use this value when regenerating the PMT for the passthrough muxer, and also include it in the HTSP stream description messages.
Add saving/loading of audio_type, and also display it in the webui
Bump HTSP protocol version to 11 for the recent transcoding changes and the addition of the audio_type field