allow local change of "threshold" - setting in ui

current state

• key settings of the intrpretation feature can only be set server-wide (html5-config-yml)
• it is not possible to adapt to different audio-levels of different participants / translators

goal

• make setting threshold - accessible for interpreters to fine-tune while interpreting
• show local ui-feedback to the interpreter, when the speaking-detection is triggered
  • without local feedback, it would be hard to effectively fine-tune the setting

how to do it in ui?

• threshold setting could be in the sidebar "languages" where languages are added
  • this does not depend on the active language channel
  • have a small info-text on how to use (see comment in #85 (closed) )
  • show the current value as a number for the interpreter to make note of it and reuse the same setting in another session
• local feedback in ui could be a speaking-indicator like the normal indicators
  • in a different color or with prefix-text or aligned at the right border of the window
  • only shown locally -> no state-synchronisation with server is neccesary