Disallows any other actions than consent accept or reject after a recording is started.

changelog: ignore

Add all current text files and regenerated the audio message.
There is now a script in the tools folder to automate the generation.

closes #15

Default mute made dail-in UX much worse
But add a new usage message placeholder

This reverts commit 5bef2a98.

Closes: #27

To mute the audio stream inside the gstreamer pipeline a `volume` element
mutes the audio stream which is toggled on receiving the dtmf key '1'.

Simulatiously an `update_media_session` message is sent via the websocket to
signal the muting of the microphone, providing the information about the muting
to all other participants.