Do not access JitsiConference's eventEmitter, the functionality of
interest is publicly available through other methods.

JitsiConference passed in the constructor and adding all events happen inside the feature.

As I see no hidden meaning in the current non-preservation of
alphabetical order, I prefer to facilitate scanning (in the fashion of
searching in a dictionary).

Fires event only once when the user is muted, if he unmutes and then mutes back again a new event will be fired if local talking is detected.