Use Opus for voice messages instead of Vorbis

[Ingvix]

It seems at least on some devices, probably mostly Apple ones, with the official Telegram app Vorbis files refuse to play for whatever reason ¯\_(ツ)_/¯, and the official app seems to use Opus format, so for wider compatibility Fernschreiber should maybe prefer it as well, I think?

[Wunderfitz]

Opus is not supported by default with the Qt library on SFOS. With SFOS 4.5 we only have the following options: audio/vorbis, audio/speex, audio/PCM, audio/FLAC

If we want to use Opus, the library needs to be integrated in Fernschreiber which is a considerable effort. No time on my side for that at the moment, but if someone wants to take it, I'm happy to integrate it.

[yusssufff]

Possible idea: Using one of the currently allowed codec (audio/speex, audio/PCM or audio/FLAC) that can also be decoded by ios. For example speex.

So the idea would be then to replace Vorbis by Speex (its even more adapted to coding voice than Vorbis)